An urgent call for help was also sent to New Zealand and Victorian state Premier Steve Bracks said he hoped about 40 remote-area specialist firefighters would arrive ahead of four days in which temperatures were tipped to soar to 40 degrees Celsius (104 Fahrenheit).

"It is a critical time now, but it is more critical as we approach this weekend," Bracks told reporters. "It's going to be one of our most difficult fire weekends in the history of this state."

Firefighters say Australia faces an extreme fire danger this summer after a worsening drought left rural areas bone dry. Scientists fear climate change will bring more frequent higher temperatures and less rainfall to the country.

Authorities said the blazes stretching 150 kilometres (93 miles) from the central King Valley to the southern coast could destroy more than 600,000 hectares (1.4 million acres) in coming days as fires merged in the face of strong winds.

A 25-kilometre-wide smoke plume covered Australia's east coast in photos taken from space and shown in newspapers.

Prime Minister John Howard promised Bracks whatever help was needed to fight the fires.

"The situation in Victoria is very serious indeed," Howard told the nation's parliament.

Fire authority spokesman Greg Leach said at least seven towns were under immediate threat.

"We had a number of larger fires merge overnight. We've had 10 years of drought in Victoria and the forests are extremely dry, and we are seeing fire behaviour that we haven't witnessed before," Leach said.

In neighbouring New South Wales there was some relief with the discovery that large fires burning there had not destroyed one of the healthiest remaining colonies of koalas in the country, as earlier feared.

Leach said three houses had been destroyed in Victoria and residents in Dargo, Licola, Bairnsdale and Maffra towns would have to decide whether to flee or fight approaching blazes.

The Dargo blaze had linked with another to form a front stretching more than 15 kilometres.

In January 2005, the deadliest bushfires in 22 years killed nine people in South Australia.

Four people were killed and 530 homes destroyed in Canberra in 2003. That same year, bushfires fuelled by drought ravaged a slice of Australia three times the size of Britain.