Three crew members have been confirmed dead. The deceased were US residents.
The aircraft, a C-130 large air tanker, was on contract with the NSW RFS.
Contact had been lost as the plane fought fires in the Snowy Monaro area.
“This afternoon, shortly before 1.30pm we lost contact with one of our large air tankers,” said RFS Commissioner Shane Fitzsimmons.
“Tragically there appears to be no survivors as a result of the crash down in the Snowy Monaro area.
“It impacted heavily with the ground and initial reports are that there was a large fireball associated with the impact of the plane as it hit the ground.”
NSW Premier Gladys Berejiklian said thoughts, prayers and heartfelt condolences were with the families of the victims, who were experienced aviation crew members.
“Today’s a reminder of how every single person who is defending life and property is at risk because of the dangerous circumstances,” said Berejiklian.
“The firefighting community around NSW, Australia and the world is very tight-knit, and I know many people have been impacted by the tragic news this afternoon.
“Our thoughts are not just with the families and friends and loved ones, but also for anybody who feels impacted by what’s unfolded this afternoon.”