Authorities in the southeastern state of Victoria on Saturday afternoon issued emergency "leave now" and "watch and act" warnings for several communities in the state's west and southwest as crews responded to out-of-control fires, reports Xinhua news agency.

"Don't wait, leaving now is the safest option," the Country Fire Authority said.

"Conditions may change and get worse very quickly. Emergency services may not be able to help you if you decide to stay. By choosing to stay, you and your family may be at risk of serious injury or death."

The Bureau of Meteorology forecasted high, extreme or catastrophic fire danger for much of southern and eastern Australia on Saturday, with high temperatures exacerbated by strong winds.

More than 20 fire trucks were deployed to fight a fire threatening the small Victorian town of Dereel, approximately 100 km west of Melbourne.

Authorities declared a total fire ban in northwest Victoria on Saturday, and the entire state was advised to be on alert.

"Because we've had such dry conditions for a number of months in a row, what we are anticipating is where there are strong winds, that can mean that a fire may spread or start in parts of the state where we haven't got the total fire ban," Luke Hegarty from the State Control Center told the Australian Broadcasting Corporation.

Conditions were expected to ease on Sunday, with heavy rainfall forecast for much of Victoria.