Victoria has sweltered through its hottest December day on record, with two towns falling just short of 48C.
Horsham, in the state's west, and Hopetoun, in the northwest, recorded 47.9C on Friday afternoon, exceeding the previous December record of 46.6C at Robinvale on New Year's Eve 1976.
Cape Otway, on the Great Ocean Road, also recorded its hottest day of 43.4C, smashing a record set more than 150 years ago.
Melbourne's temperature fell short of the forecast 44C, reaching a maximum of 43.4C, the capital's hottest day since 1876.
"I know we talk a lot about records but it just helps us put in context the extent and unseasonality of the heat. It's just not something we'd normally see in December," the Bureau of Meteorology forecaster Adam Morgan said.
He said the hottest part of summer is usually in January.
There will be no reprieve from the heat until a cool change at about midnight.
"The cool change is still on track and is still later than anyone would want," bureau senior meteorologist Keris Arndt said.
"We will slowly cool down with the sun going down but we won't have any cool air until about midnight."
Victoria's Chief Health Officer Brett Sutton warned it could make for an uncomfortable night.
"Lying in bed, people's core body temperature can still increase if the temperatures inside their home are significant," he told reporters.
"Bear in mind people may have a kind of hangover tomorrow with headache and fatigue or even heat cramps or exhausting, racing heart, sweating."
Smoke from the NSW bushfires blanketed Melbourne for most of the day and may also cause some health issues.
The air quality in some parts of Victoria, including Melbourne's suburbs of Bentleigh, Keysborough and Sandringham, was rated "unhealthy" by AirWatch.
East Gippsland, where fire crews are battling several blazes, is experiencing "very poor" to "hazardous" air conditions, according to the Environment Protection Authority Victoria.
"Smoke is never good for you and there is no safe level. So we really say to everyone - minimise your exposure," Dr Sutton said.
He urged people to check on the young, elderly, pregnant woman and those with respiratory conditions.
Australian Associated Press