A water tanker plane fighting wildfires in Australia has crashed killing three American crew members, officials have said.

The C-130 Hercules plane went down in the Snowy Monaro region in the state of New South Wales (NSW).

The state’s Premier Gladys Berejiklian expressed her condolences to the families of the three crew members, who were flown in as part of an international assistance effort to fight the devastating wildfires.

“Our thoughts & heartfelt condolences are with their families & the tight knit firefighting community,” Ms Berejiklian tweeted.

NSW Rural Fire Service Commissioner Shane Fitzsimmons told reporters the plane had crashed amid “a large fireball”.

He confirmed all three crew members aboard were US residents.

“Unfortunately, all we’ve been able to do is locate the wreckage and the crash site and we have not been able to locate any survivors,” he said.

Ms Berejiklian said more than 1,700 firefighters and volunteers were currently fighting fires in the state as Australian wildfire crisis – which began in September – continues.

Canberra Airport was closed on Thursday owing to nearby blazes, and residents south of Australia’s capital were told to seek shelter.

“Arrivals and departures are affected due to aviation firefighting operations,” the airport authority said in a tweet.

Five fires burning in NSW were being described as at an “emergency warning level”.