Heat expected to return to Melbourne in time for Boxing Day Test

Australian Prime Minister Malcolm Turnbull dances with attendees during the annual Wayside Chapel Christmas lunch and street party in Kings Cross, Sydney. Photo / AAP

Australians are celebrating Christmas, some in relative chilly conditions, and others in sweltering heat, with lunches, fun runs and backyard cricket.

People in Melbourne, Sydney and Hobart began the day in mild conditions, with drizzle and winds expected later.

Melbourne can expect a top of 22C, Hobart is expected to hit 21C and Sydney will experience an unseasonally low top of 23C.

But the lack of sun won't deter revellers from their backyard barbecues, or heading down to the beach for their Christmas swim.

The heat is expected to return to Melbourne tomorrow, in time for the expected large crowd at the Boxing Day Test, with the city set to hit a maximum of 29C.

Prime Minister Malcolm Turnbull has paid a visit to the Wayside Chapel, serving Christmas lunch to Sydney's homeless.

Turnbull thanked volunteers and posed for selfies at the event, which serves up about 1000 meals for Sydney's less fortunate. "Merry Christmas, it's wonderful to be here with you all, I want to thank in particular all the volunteers - the people who work at the Wayside, it is a great excessive in practical, unconditional love," Turnbull told the crowd.

A surge of energetic people around the country held off unwrapping presents to take part in a 5km fun run part of their Christmas morning tradition. Huge numbers of runners took to 73 free ParkRun events around the country.

Almost 800 people hit the pavement in Brisbane's South Bank ParkRun despite the mercury reaching 28C at their 7am start time. A sizzling 34C in Brisbane is expected to drive people to the beach to cool down. Some parts of Queensland will hit steamy tops of 40C, with Birdsville in the remote outback near the South Australia and Northern Territory border likely to hit 45C.

Adelaide can also expect glorious weather for barbecues, with blue skies and temperatures up to 29C while Perth is expecting a sunny top of 33C.

- AAP