AN explosion of lava that poured through the roof of a tour boat off Hawaii's Big Island has injured 23 people.
The Hawaii County Fire Department said a woman in her 20s was in a serious condition with a broken thigh bone after the horror event on Monday.
Three others were in stable conditions at a hospital with unknown injuries.
The rest of the passengers suffered burns, scrapes and other superficial injuries.
They were aboard a tour boat that takes visitors to see lava plunging into the ocean from a volcano that has been erupting for two months.
Firefighters said the lava punctured the boat's roof, leaving a gaping hole.
Officials have warned of the danger of getting close to lava entering the ocean, saying the interaction can create clouds of acid and fine glass.
Several companies operate such tours despite the dangerous hazards.
The US Coast Guard in May set up a safety zone where the lava flows into the ocean off the Big Island.
It prohibits boats from getting closer than 300m from ocean-entry points.
The agency allows experienced boat operators to apply for a special license to get up to 50m from where lava sizzles into the sea.
The molten rock is coming from the Kilauea volcano, which has been erupting from a rural residential area since early May and has destroyed more than 700 homes.
But until now, the only serious injury was to a man who was hit by flying lava that broke his leg.
Officials were interviewing injured passengers in hospital.