The death toll in the White Island volcanic eruption is set to rise from five as New Zealand police confirmed "no signs of life have been seen at any point" on the island.

Scott Morrison has warned the nation of "difficult days ahead" after confirming 11 Australians remained "unaccounted for" and three are dead following the NZ volcano eruption.

The first victim was identified as Hayden Marshall-Inman, an experienced guide for White Island Tours from Whakatane in the North Island, who "passed away doing the one thing he loved", his brother Mark wrote on Facebook.

Up to 50 tourists were still on the private island off the country's North Island when the volcano erupted, among them passengers on an Ovation of the Seas cruise ship, which left Sydney on December 4.

According to New Zealand's geological monitoring agency, GeoNet, the eruption sent ash plumes about 3.7km into the air.

A New Zealand Defence Force ship was scheduled to approach the island this morning and deploy drones and observation equipment, while a police identification team was assembling.

Mr Morrison said there was still "no comprehensive or confirmed information" about the wellbeing of all those impacted by the volcano.

"It will take time for us to get a clear indication and we must be patient," he said last night.

"There are still people who are unaccounted for, including Australians.

"We are working to confirm this information with NZ authorities."

Mr Morrison said the government has so far been able to confirm a "number of Australians" who were in hospital.

"We hope to know more in the morning, however we must prepare for some difficult news in the days ahead."

New Zealand police painted a bleak outlook for any survivors of the shocking explosion.

"Based on the information we have, we do not believe there are any survivors on the island," New Zealand police said in a statement.

"Police believe that anyone who could have been taken from the island alive was rescued at the time of the evacuation."

The view came after police and rescue aircraft performed a number of reconnaissance flights over White Island after the eruption.

VICTIM REMEMBERED AS HAVING THE 'KINDEST HEART'

An experienced guide for White Island Tours has been identified as one of the five people confirmed dead.

Hayden Marshall-Inman, from Whakatane in the eastern Bay of Plenty Region, was praised by former Whakatane mayor Tony Bonne as "a young energetic man, who has lost his life".

His brother Mark confirmed Hayden's passing on Facebook, saying: "Family and friends, very sad news this evening. My bro Hayden Marshall-Inman has passed away doing the one thing he loved. Thanks for all your messages. I'll be in touch when we know more.

One friend, Grant Bateson, said Hayden was "truly one of the good guys".

"So sorry to hear bro. He was such a top man. He's left a huge impact on this world."

Another friend, Julie Lockett, remembered his generosity.

"I worked at the Ohope 4 Square and whenever he came in and made a purchase he always gave us $5 to pay towards the next person's groceries, he had the kindest heart, it was never about him, he definitely created a ripple affect of happiness to others, a very likeable guy."

White Island Tours Limited released a media statement saying it was "deeply saddened" at the volcano's significant eruption.

"Devastation is an understatement," Paul Quinn, Chairman for White Island Tours said.

"This is a terrible tragedy and our thoughts and prayers are with everyone who has been impacted."

White Island Tours' website has been taken down and replaced with a message which says they're currently experiencing an emergency.

ISLAND 'UNSAFE TO GO BACK'

Rescuers were told yesterday it was unsafe to go back to the island. The volcano monitoring organisation GeoNet said there had been "a steady decline in activity since the eruption", although one volcanic expert said another eruption soon was a possibility.

NZ Deputy Commissioner John Tims said emergency services are unable to access the island.

"The island is unstable... the physical environment is unsafe for us to return to the island," he said.

"It is important that we consider the health and safety of those that will return to the island."

The five people killed were taken off the island today and are of a "range of nationalities," he said.

The New Zealand Defence Force sent personnel to assist and a Royal New Zealand Air Force P-3K2 Orion aircraft flew over White Island carrying out surveillance over the area, and two NH90 helicopters flew to Whakatane to assist.

After a press conference with Prime Minister Jacinda Ardern, he said there will likely be more fatalities.

"At this stage it is too dangerous for police and rescue to go on to the island... the island is currently covered in ash and volcanic material," he said.

"A number of people have been taken to Whakatane Hospital and Middlemore Hospital."

Ms Ardern said there were "a number of tourists" from her country and overseas on the island at the time.

"I know there will be a huge amount of anxiety for those who have loved ones on or around the island at the time. I can assure them police are doing everything they can," Ms Ardern said.

Ms Ardern and Civil Defence Minister Peeni Henare travelled to nearby Whakatane last night.

Volcanic expert Dr Ken Gledhill from GNS Science in New Zealand described the eruption as a "throat clearing".

"It's not a particularly big eruption, almost like a throat-clearing eruption and that's probably why material won't make it to the mainland," Dr Gledhill said.

He also said it had quietened down but they cannot be certain there won't be another eruption in the next 24 hours.

Anyone concerned about loved ones can call a 24-hour DFAT emergency number on 1300 555 135 from within Australia or +61 2 6261 3305 from overseas.

The Family Links website was activated by the New Zealand Red Cross at the request of New Zealand Police for families to register missing loved ones. More than 20 Australians were listed as of early Tuesday morning Australian time.

AUSSIE CRUISE SHIP INVOLVED

Photographs taken just before the volcano erupted show two tour groups from a cruise liner that left Sydney last week walking on the crater floor.

Many of the people on the island at the time of the eruption were from the Ovation of the Seas cruise ship.

The captain of the ship announced to passengers that a group of guests and one crew member were on the island as the eruption occurred.

He told passengers on-board they're waiting on information from the government to see what's happened, a passenger said.

The ship's owner, Royal Caribbean Cruises, said: "Ovation of the Seas will remain in port as long as needed to assist with the situation."

One passenger said people were silent after the captain delivered the message and a helpline has been opened up on the ship for those who are missing loved ones.

The ship left Sydney last week on December 4 for its 12-day voyage and docked at Tauranga where passengers joined local tours to the volcano. There are 4579 passengers and 1595 crew on board.

It was scheduled to arrive at Wellington tomorrow before cruising around the South Island before heading back to Sydney.

A spokeswoman from Royal Caribbean International, which owns the luxury liner, confirmed passengers from the ship had taken local excursions to the volcano.

Ovation of the Seas passenger Nigel Walker and his family from Wollongong in NSW told The New Zealand Herald his thoughts were with those who were injured and unaccounted for.

"It's tragic...I was only saying to my mother-in-law before the cruise that White Island would be a great pĺace to visit. "

The New Zealand Cruise Association chief executive Kevin O'Sullivan said it was very concerned about some passengers from the Ovation of the Seas.

"Our primary concern right now is with the wellbeing of the passengers and all those involved. We would like to extend our heartfelt concern to the passengers and their families," Mr O'Sullivan said.

"Our hope is that everyone will be recovered quickly and unharmed, but at this time we have no further information."

EYEWITNESSES SHOCKED BY BLAST

American tourist Michael Schade said he had only just left the island less than 30 minutes before it exploded and was "waiting for the boat to leave" when he witnessed the carnage.

"My god, White Island volcano in New Zealand erupted today for (the) first time since 2001. My family….. Boat ride home tending to people our boat rescued was indescribable," he said.

"Those are some of the people put boat picked up. Praying for them and their recovery. Woman my mom tended to was in critical condition but seemed strong by the end. The helicopters on the island looked destroyed."

Mr Schade described the incident as "hard to believe" and said: "Our whole tour group were literally standing at the edge of the main crater not 30 minutes before. My thoughts with the families of those currently unaccounted for, the people recovering now, and especially the rescue workers."

Calvin Kingi, who works at White Island Tours, posted a picture to Facebook and said: "White island just erupted as we left, we have our work mates and a tour still on the island, I hope they (are) ok."

Brazilian tourist Allessandro Kauffmann was exploring the volcano five minutes before it erupted.

He told News Corp a tour group of about 20 people stepped onto the island as his boat left.

His close brush with death has left him rattled.

"I am so shocked," Mr Kauffmann said.

"They had two tours. Ours all went well as we managed to get off the volcano before the eruption.

"Already the second tour failed to leave in time.

"It was an unbelievable situation because we left around five minutes before the eruption."

Mr Kauffmann captured dramatic footage of the enormous explosion and people scrambling for safety on his boat.

A man on a loudspeaker can be heard yelling: "I need everyone inside the boat right now" as giant plumes of smoke billow nearby.

Other passengers can be heard asking for an inhaler due to breathing concerns.

Mr Kauffman said his boat stayed to support those on the volcano at the time of explosion.

Melbourne dad Mathew Merington said he and his kids are "praying" for those caught up in the tragedy.

The family stayed onboard the Ovation of the Seas ship as others ventured out to the volcano.

Mr Merington said other tourists spent the day exploring the mainland and may not be aware of the unfolding disaster.

"It's sad but we are praying for the impacted ones," he told the Herald Sun.

"My kids are doing okay."

CAMERAS CAPTURE LAST MOMENTS BEFORE ERPUTION

The White Island Crater Rim camera, held by GeoNet, showed a string of people visiting the crater at that time.

Subsequent shots from the camera, displayed online every 10 minutes, show the blast rendered the camera inoperable.

A Department of Foreign Affairs and Trade spokesperson said: "Australia's High Commission in Wellington is making urgent enquiries with local authorities to ascertain if any Australians were affected by the eruption near White Island in New Zealand."

The volcano, located around 40 kilometres offshore of the Bay of Plenty, sent huge amounts of white smoke - most likely steam - into the air.

St John director of operations Norma Lane said 11 helicopters and 12 ambulances were dispatched.

"One helicopter with paramedics and St John Medical Director Dr Tony Smith on board spent a short time on the island assessing the scene. Staging points were set up at Whakatane Airport and Whakatane Coastguard base to assess and triage patients. In total St John responded with 11 helicopters and 12 ambulances to treat and transport patients to various hospitals including Whakatane, Tauranga, Middlemore and Auckland City, by air and road.

"St John has treated patients with injuries ranging from critical and serious through to moderate and minor. It has been an exceptionally complex scene and our paramedics, both frontline and working in our Clinical Communications Centre, have done an outstanding job in very difficult circumstances.

"We will continue to support the operation and debrief with our frontline teams in the coming days."

GeoNet agency said a moderate volcanic eruption had occurred and raised its alert level from two to four, on a scale where five represents a major eruption.

Police asked people to avoid areas on the North Island that were close to the eruption, including the Whakatane Heads and Muriwai Drive areas.

White Island sits about 50 kilometres offshore from mainland New Zealand.

Whakatane mayor Judy Turner confirmed the eruption produced injuries.

Geological hazard trackers GeoNet had registered moderate volcanic unrest on the island for weeks.

Whakaari is New Zealand's most active cone volcano, and frequently visited by tourists.

The local council says New Zealand Police and Bay of Plenty Civil Defence are working together to respond.

GeoNet says it is New Zealand's most active cone volcano and about 70 per cent of the volcano is under the sea.

TOUR CHOPPER ALSO GOES DOWN

The NZ Herald also reports a White Island tour company left one of its helicopters behind on the island.

Five people had flown with Volcanic Air to the island, but all are accounted for and have arrived back in Whakatane by boat.

Twelve people were killed on the island in 1914 when it was being mined for sulphur. Part of a crater wall collapsed and a landslide destroyed the miners' village and the mine itself.

The remains of buildings from another mining enterprise in the 1920s are now a tourist attraction, according to GeoNet.

The island became a private scenic reserve in 1953, and daily tours allow more than 10,000 people to visit the volcano every year.

The island is also known by the indigenous Maori name Whakaari.

An AirNZ media spokeswoman said no flights were delayed or cancelled as a result of the eruption.