The Boeing 737 Airliner had been fighting fires in the area when the plane went down about 4.15pm (7.15pm AEDT), the Western Australian Department of Fire and Emergency Services (DFES) confirmed on Monday evening.
Two people on board the plane managed to escape.
A helicopter airlifted them to Ravensthorpe Airport before they were taken to a local medical facility.
The Australian Maritime Safety Authority (AMSA) said it “detected an emergency beacon activation from the firebomber” approximately 185 kilometres west of Esperance.
“There were no other crew aboard the firebomber when it crashed,” AMSA said in a statement issued on Monday evening.
The National Large Air Tanker had departed Busselton-Margaret River Airport, bound for the bushfire, about 3.30pm today, 45 minutes before the crash.
The Australian Transport Safety Bureau has launched an investigation into the accident.
A team of investigators from Perth and Canberra is heading to the crash site to recover data and evidence.