'A Ball Of Flames': Mayday Call From Plane Crash That Killed Three American Firefighters

A distressed mayday call from firefighters on the ground when three American first responders crashed in their waterbomber on Thursday shows how quickly the tragic accident happened.

Just after 2pm, a firefighter could be heard calling into the RFS command centre.

"Fire comms…message red speak to your captain. Message this is red," a distressed voice said.

The man says the word "crashed" before the audio cuts out briefly.

"Yeah fire comms…it's just a ball of flames. Over."

The trio, who have been in Australia since November helping to put out bushfires, set out from Richmond RAAF Base just after midday to work on a blaze in the Snowy Mountains, but never made it back.

They are all understood to have died in the crash, and their families are on their way to Australia.

Investigators will begin piecing together the events that caused the large aerial water tanker to crash in the Snowy Mountains region on Thursday afternoon.

United States ambassador Arthur Culvahouse said he was "deeply saddened" by the news.



Three Dead After Firefighting Plane Crashes In NSW

Flags will be flown at half mast on Friday in memory of three people killed in a firefighting aircraft crash in the NSW Snowy Mountains region.

"The brave Americans who died near Snowy Monaro died helping Australia in its time of need," he said in a statement.

"Thank you Australia for your sympathy and solidarity."

Foreign Affairs Minister Marise Payne paid tribute to the US firefighters and said she had passed on Australia's condolences to Culvahouse.

"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," Payne said in a statement.

"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."

Investigators from the Australian Transport Safety Bureau will travel to the crash site to start collecting evidence.

"Should a critical safety issue be identified during the course of the investigation, the ATSB will immediately notify relevant stakeholders so appropriate and timely safety action can be taken," the ATSB said in a statement.

NSW Premier Gladys Berejiklian said Thursday's lethal conditions showed the unprecedented fire season was "far from over".

"We can't thank people enough for continuing, not withstanding the conditions, to put their safety at risk to protect lives and property of others," she said.

A closed road sign is seen on the road to Peak Hill where a three American firefighters have died after a waterbombing air tanker crashed while fighting fires. Image: AAP

Fire danger ratings are forecast to drop on Friday as milder weather conditions set in across NSW.

Authorities will contact the families of the plane crash victims before they release their names to the public.

The plane, known as Zeus, was owned and operated by Canada-based company Coulson Aviation and contracted to the RFS.

The company's owners are travelling to Australia and are expected to arrive later on Friday.