A massive blaze in the Grampians National Park in Victoria state alone has burnt through more than 120,000 hectares (300,000 acres) of land, an area the size of Hong Kong, and now has a fire front of 350 km. It has destroyed 24 homes and killed 59,000 sheep.

As the blazes rained burning embers on several towns and communities, the Bureau of Meteorology issued on Thursday a severe thunderstorm warning for Victoria.

"The thunderstorms are a bit of a double-edged sword for firefighters," Victorian Country Fire Authority Deputy Chief Officer Graham Fountain told Reuters.

"They can bring some welcome relief to assist with the containment of the fire itself if there is some decent rain associated with them. But at the same time they can hamper efforts to back burn and make tracks unpassable and slippery."

The Victorian blazes have already left three people dead, a father and son whose car was engulfed in flames after they crashed while racing to save a family home, and a firefighter who was killed when his tanker rolled during mopping-up operations.

BURNING OUT OF CONTROL

Fountain said the Bureau of Meteorology has forecast decent rain in the coming days, but it was unsure whether it would arrive with this forecast thunderstorm weather front.

"If it is just strong gusty winds it can assist to whip the fire up and drop more burning embers ahead of the perimeter."

As Australians celebrated their national day on Thursday, marking the arrival of the first European settlers in 1788, hundreds of firefighters were battling blazes in temperatures peaking near 40 Celsius (104 Fahrenheit).

Blazes were also burning out of control in the southern island state of Tasmania, but were not threatening property, and bushfires in Western Australia state appeared to have eased with the arrival of some rain.

Earlier this month, several homes north of Sydney in New South Wales and in western Victoria were destroyed by bushfires.

Australia is scarred by bushfires every summer and every few years bushfires blaze into major cities which have fingers of bushland weaving through suburbs.

In January 2004, the deadliest bushfires in 22 years killed nine people and injured dozens in South Australia. The blazes were the worst since Ash Wednesday bushfires claimed 75 lives in South Australia and Victoria in 1983.