Crash site investigators have retrieved the black box from a downed firefighter aircraft which crashed in southern NSW, killing its American crew, and hope to access it by Sunday.

US aerial firefighters captain Ian McBeth, first officer Paul Hudson and flight engineer Rick DeMorgan Jr died when their C-130 Hercules hit the ground during a "routine" waterbombing operation.

NSW Rural Fire Service Commissioner Shane Fitzsimmons said there was a "large fireball" when the aircraft crashed.

Photos and videos taken on Friday showed emergency services and crash site investigators combing the wreckage as part of what will be a months-long inquiry into the circumstances leading to their deaths.

The water-bombing aircraft dropped fire retardant before it went down. ( Supplied: NSW Police )

Air crash safety investigators have recovered the C-130's black box, which typically records the last two hours on the flight deck.

Australian Transport Safety Bureau (ATSB) Chief Commissioner Greg Hood said the voice recorder was found at the tail end of the aircraft.

"We removed the cockpit voice recorder and we’ve removed that piece of equipment to the ATSB’s technical facilities in Canberra," Mr Hood said.

It's hoped the black box will shed some light into the final minutes before the large air tanker crashed in bushland north-east of Cooma.

ATSB investigators retrieved the black box from the wreckage this morning. ( Supplied: ATSB )

"It could be useful or it might not be very useful, it depends on what was said.

"We remain hopeful."

Mr Hood said officers will be able to access data on the black box by Sunday.

Officers have now started the "painstakingly meticulous" process of mapping the crash site for debris.

The front of the plane appeared to been obliterated during the impact. ( Supplied: NSW Police )

Drone vision shows only the tail of the repurposed military aircraft remained intact.

A darkened trail can be seen leading into the trees, with debris and small parts of the aircraft scattered across the dry landscape.

The plane, which can carry 15,000 litres of water or fire retardant, departed RAAF Base Richmond, in Sydney's west, about 12:05pm on Thursday.

Flight data showed the C-130 suddenly stopped moving just after 2:00pm in an area called Peak View.

The aircraft was being used to protect properties from the Good Good fire in Cooma. ( Supplied: NSW Police )

NSW Police said they recovered the bodies of the US crew this morning. ( Supplied: NSW Police )

The RFS said this happened just shortly after the aircraft released fire retardant over a blaze in Snowy Monaro.

It said the plane was protecting properties from the Good Good fire, which has so far burnt through 41,510 hectares of land in the Snowy Monaro region of NSW.

Rumours were swirling online that the debris and flames from the crash were responsible for the destruction of the Kalandan wildlife sanctuary, near Jerangle.

While the sanctuary's buildings were destroyed and a vast majority of the native animals likely killed, the RFS said it was yet to find a direct link between the two events.

NSW Police and military aircraft at the site of the C-130 Hercules crash near Cooma. ( Supplied: NSW Police )

"The plane crash did occur on an active fireground," said RFS spokesman James Morris.

"It's too early to tell at this stage, but there was already significant fire activity and the likelihood of [this] fire burning through [the sanctuary] was almost 100 per cent chance."

Allison Cairns, the co-founder of Animal Rescue Cooperative, who works with the sanctuary owner, said the crash was "not a contributing factor" to its destruction.

Ms Cairns estimated thousands animals — including kangaroos, wallabies, koalas and goannas — were killed by the fires.

The Good Good fire near Cooma continues to burn out of control. ( Supplied: NSW Police )

This morning, NSW Police said they had recovered the bodies of the three crew members and the Federal Government has promised to repatriate them back to the United States as soon as possible.

The crash investigation will be led by the Australian Transport Safety Bureau (ATSB), while the Civil Aviation Safety Authority (CASA) will provide support as requested.