The authorities said they lost contact with the aircraft which was water-bombing the bushfires in the southeastern state of New South Wales on Thursday.
According to the statement sent on Twitter, the New South Wales Rural Fire Service is investigating the incident.
Limited information about the occupants of the aircraft was provided.
Fire departments across the state have been battling the raging wildfires for months now.
The disaster was exacerbated by extreme temperatures and windy conditions.