SYDNEY (AP) — Three American firefighting airplane crew members were killed Thursday when the C-130 Hercules aerial water tanker they were in crashed while battling wildfires in southeastern Australia, officials said.

New South Wales Premier Gladys Berejiklian confirmed the deaths in the state’s Snowy Monaro region, which came as Australia grapples with an unprecedented fire season that has left a large swath of destruction.

Canada-based Coulson Aviation said in a statement that one of its Lockheed large air tankers was lost after it left Richmond in New South Wales with retardant for a firebombing mission. It said the accident was “extensive” but had few other details.

“The only thing I have from the field reports are that the plane came down, it’s crashed and there was a large fireball associated with that crash,” Rural Fire Service Commissioner Shane Fitzsimmons said.

Foreign Minister Marise Payne said she had conveyed Australia’s condolences to U.S. Ambassador Arthur Culvahouse Jr.

“Our hearts go out to their loved ones. They were helping Australia, far from their own homes, an embodiment of the deep friendship between our two countries,” she said in a statement.

Payne added: “Thank you to these three, and to all the brave firefighters from Australia and around the world. Your service and contribution are extraordinary. We are ever grateful.”

The tragedy brings the death toll from the blazes to at least 31 since September. The fires have also destroyed more than 2,600 homes and razed more than-25.7 million acres, an area bigger than the U.S. state of Indiana.

Coulson grounded other firefighting aircraft as a precaution pending investigation, reducing planes available to firefighters in New South Wales and neighboring Victoria state.