Regional Express (Rex) said it now believed it would be able to survive for at least six months "if the current situation does not deteriorate much further".

It said on Wednesday the exact network changes would be announced in coming days, and expected about 40 per cent of capacity would be cut and some routes dropped.

Rex, which has a wide-ranging network of routes including Burnie-Melbourne and King Island services, had warned in an open letter to Deputy Prime Minister Michael McCormack on March 16 that regional carriers would not last more than six months without help and the weaker ones only had weeks of reserves.

Mr McCormack announced relief measures the next day, including waiving of air traffic control charges, fuel excise and regional aviation security charges.

"Michael and the Morrison Government have demonstrated firm and decisive leadership in putting together this package within such an incredibly short timeframe," Rex executive chairman Lim Kim Hai said.

"The situation is extremely dynamic and Australia is fortunate to have a government that is very proactive and nimble.

"Rex and all Australian carriers owe the Morrison Government a huge debt of gratitude for providing this precious lifeline without which all regional carriers, and, we believe, some domestic ones too, will go into administration."

Mr Lim said Rex was disappointed the package did not include a sovereign guarantee of new bank loans to get regional carriers through "the period of extreme negative cashflow".

He said he hoped that would be included in a second stage of assistance.

Rex said it had spoken to unions and was grateful unions and staff were "firmly supportive of the draconian measures that need to be implemented in these dire circumstances".