Three US residents died in a firefighting aircraft crash in Australia, authorities have confirmed.

The large air tanker and crew were reported missing in southern New South Wales shortly before 13:30 local time (02:30 GMT) on Thursday.

The cause of the crash is not yet known.

NSW Premier Gladys Berejiklian said the plane crashed in the Snowy Mountains, two hours south of the capital, Canberra.

“Our thoughts and prayers and heartfelt condolences go to their families,” she told reporters on Thursday.

“Today, again demonstrates the fire season is far from over.”

The three crew members have not been identified but officials said they were US residents.

The NSW Rural Fire Service said the crew had been contracted to Australia to help fight the bushfires this season.

The Hercules C-130 water-bombing aircraft had been deployed to fight a severe blaze in the region.

More than 80 blazes are raging across the state amid a return of high temperatures and strong winds.

It was unclear what had had caused the plane to crash, said Commissioner Shane Fitzsimmons.

“Initial reports are that there was a large fireball associated with the impact of the plane as it hit the ground,” he said.