A rugby league club's roof collapsed on Boxing Day in Sydney with hundreds of people inside the venue.

St Marys Rugby League Club in Western Sydney was battered by storms on Saturday afternoon, culminating in the roof collapsing shortly after 5.15pm.

Fire and Rescue NSW superintendent Scott Dodson said there were 400 guests of the club at the time of the collapse.

He said there were no reported injuries but an ambulance was on-site as a precaution.

"From what I've heard the club staff did a fantastic job to get everyone out safe," he said.

Superintendent Dodson said the cause was a build-up of hail blocking the guttering and preventing rainwater from flowing away.

The weight of the water caused a partial collapse of the internal ceiling.

"Fire and Rescue worked with building management to isolate the electricity and make it safe," he said.

Two trucks with eight Fire and Rescue NSW firefighters attended the incident to assist staff and building management with the evacuation.

Chief operating officer Stewart Graham said the club intended to open on Sunday but some areas may be closed.

"There's a bit of clean-up to do," he said.

"Hopefully we'll be reopening tomorrow morning.

"There's no structural damage to the roof itself, it's more internal ceiling damage."

St Marys Rugby League Club includes four restaurants: Millys, Ironbark Terrace and Pizzeria, Signatures Seated Buffet, and Waterstone Grill.

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