Australian heatwave fans bushfires, Melbourne endures hottest day in 17 years

A major heatwave across Australia's southeast stoked bushfires, forced hundreds of residents in rural towns to evacuate and brought record-breaking temperatures, with Melbourne recording its hottest day in nearly 17 years.

Temperatures in parts of Melbourne, the capital city of Australia's second-most populous state of Victoria, exceeded 45 degrees Celsius.

Towns in Victoria's northwest Mallee region also reached a high of 48.9 C, breaking the state record, according to preliminary data from Australia's Bureau of Meteorology.

The heatwave - the worst since the 2009 Black Saturday bushfires that killed 173 people in Victoria - raised the fire danger in some parts of the state to extreme. Many communities are still recovering from large bushfires at the start of the month, also triggered by a severe heatwave.

Chris Hardman, the chief fire officer of Forest Fire Management Victoria, said six major fires were burning, with three out of control.

He said a fast-moving blaze in the Otways region was of most concern to firefighters, burning about 10,000 hectares and destroying at least three properties.

"Firefighters did an incredible amount of work to try and contain that fire overnight ... but as the warmer weather and the inversion broke, some gusty winds came down and that fireground has spotted outside of its original containment lines," he told a news conference.

Hardman warned that strong winds up to 70 kph forecast in the evening could further spread the blaze, threatening homes.

"We will get strong south-southwesterly wind change," he said. "That fire will run, it will develop a plume, it will pick up really significant energy and we will see erratic and extreme fire behaviour."

Emergency services have door knocked about 1,100 homes and sent text messages to around 10,000 phones urging residents to leave the region, Heffernan said.

Total fire bans were declared across Victoria as officials tried to lower the risk of new fires.

Organisers of the Australian Open tennis Grand Slam in Melbourne said matches on the outside courts and roof closures would follow its extreme heat condition protocols. Wheelchair matches have been postponed to Wednesday.

In inland Victoria, temperatures in some rural towns broke local records. Hopetoun Airport and Walpeup in the Mallee region, around 477 km northwest of Melbourne, both reached 48.9 C, the highest temperature ever recorded in the state.