Defence Minister Linda Reynolds is preparing to send hundreds of navy, army and air force reservists to join the fight against raging bushfires across NSW and Queensland.

In the biggest military call-up for a civil emergency of its kind in Australia, Senator Reynolds said work was underway to call on the Australia Defence Force's (ADF) "highly capable Reserve forces" to support regular troops and volunteer and professional firefighters.

120 Reserve members are currently available in Brisbane and 130 on standby in Sydney to provide transport, logistics and other requested support if required.

She told federal Parliament on Tuesday the ADF was "actively scoping" a possible full "call-out" of reservists, under powers only ever made "in support of significant national emergencies if required to supplement ADF regular personnel".

"Defence will continue tasking discrete elements of the Army Reserves, Navy Reserves and also Air Force Reserves using existing voluntary 'call-for' arrangements, again as the circumstances require," Senator Reynolds told the Senate.