Melbourne has had its hottest Christmas Day in 18 years, with the temperature reaching 36.3 degrees at 4.30pm today.
Bureau of Metrology senior forecaster Beren Bradshaw said it was the warmest Christmas since 1998.
"It's been 18 years since we have experienced a Christmas Day with temperatures this hot," Ms Bradshaw said.
The temperature hit 36.3 degrees in 1998, but the highest on record was 40.7 degrees in 1907.
Conditions were dry this year but it was not windy.
A "watch and act" alert is in effect for Hopetoun, Banyan, Curyo, Marlbed, Watchupga, Willangie and Woomelang for a grassfire that has crossed the Sunraysia Highway, according to VicEmergency.
Bureau forecasters report there will be no significant cool change in the city until tomorrow, with temperatures to dip slightly to 24 degrees overnight.
"It's not the nicest of conditions but a cool change will push through around mid-morning on Monday," forecaster Michael Efron said. "There are expected to be showers in the afternoon on Monday, which could cause interruptions for the cricket.
The Australian Medical Association has cautioned people to stay out of the sun and stay hydrated as they enjoy Christmas festivities on the hot day.
AMA vice-president Dr Tony Bartone said the hot conditions required special precautions, particularly for older people, young children and pregnant women.
"Heatwaves are responsible for more deaths in Australia than any other type of natural disaster, and it's important to prepare for hot weather," Dr Bartone said.
The City of Melbourne has engaged the Salvation Army to extend the opening hours of its cafe to provide respite to homeless people.
More than 2000 pool passes and 240 movie tickets will also be available to help homeless people escape the heat.
"We know that 374 people died across Melbourne in one heatwave in 2009. This is higher than the annual road toll for the state," lord mayor Robert Doyle said.
At 10am on Sunday, Areti Toumbalis, her family and a friend were judging the position of the sun to set up the best picnic spot near a small group of trees on the foreshore in Brighton.
They had come from South Morang for a bayside Christmas feast of roast lamb, chicken schnitzel, couscous salads and other delights.
It was her first Christmas Day on the beach although she is a frequent visitor.
"I've come here many times. It's a nice beach, it's quiet," she said.
With AAP