Heatwave conditions have returned return to parts of Victoria today, more than a week after the state sweltered through one its hottest string of days on record.
Northern parts of the state could experience seven days in a row of temperatures above 40 degrees Celsius.
The forecast top for Geelong and Laverton is 40C.
Melbourne is expected to reach 39 degrees Celsius but the weather bureau says it could go higher.
"There's a reasonable chance we could get just up above 40C (in Melbourne) especially just ahead of the front," said Bureau of Meteorology senior forecaster James Taylor.
Mr Taylor says the heat could rival temperatures experienced during earlier this month.
"There's some chance that this heatwave could be slightly longer," he said.
"In terms of the intensity and how hot the temperatures get, will really depend on the air mass over next weekend."
The extreme weather forecast has prompted fire authorities to declare a total fire ban across the entire state today.
The Country Fire Authority's state duty officer Stephen Walls says the fire threat will be be increased by the forecast of strong winds.
"We're expecting winds, particularly in the western parts of the state, to get up around 40 kilometres an hour," he said.
"Those conditions would lead to fires being quite uncontrollable if a fire started."
Mr Taylor says the fire risk is very serious just before the change moves across the state this evening.
"It's the front that will be the real issue for fire activity today," he said.
"(We're) expecting that to make it to Port Phillip heads probably around 6:00pm and the CBD around 8:00pm and should be through the eastern surburbs by around 9:00-10:00pm tonight."
Heat prompts health warnings
Victorian Health Minister David Davis says the heat can have a serious impact on the health of the elderly.
He has asked the public to keep in contact with their older relatives today.
"It's really important that if you've got a neighbour, or a friend, or a family member who's older or vulnerable that you check in on them, that you see if there is something that can be done to help them," he said.
He has urged all people to respect the heat and avoid physical activity in the sun.
"If you are able to avoid strenuous exertion like sport or gardening at a time when the temperature is at its maximum do so. The heat can actually sneak up on anyone," he said.
Parents warned about children in hot cars
Signs are being put up at childcare centres across Melbourne to remind parents children can die in hot cars.
Ambulance Victoria responded to dozens of call-outs for children locked in cars during the heatwave earlier this month.
The chief executive of Kidsafe Victoria Melanie Courtney says one childcare franchise has joined the campaign to put up warning signs in car parks.
But she says Kidsafe wants other centres and shopping malls to come on board.
"We did see a lot of incidents a couple of weeks ago when we had temperatures exceeding 40 every day," she said.
"With another hot week this week, 39C predicted today, it can get up to 70 degrees in a vehicle, which is deadly for a child."
Heat returns to southern Australia
There are also total fire bans in place in South Australia and Tasmania ahead of forecast extreme heat.
Adelaide's maximum temperature today is expected to be 41C today 40C on Friday, 41C on Saturday and 40C on Sunday.
Temperatures in Tasmania are set to reach the high 30s and the Tasmanian Fire Service says any fires will develop quickly and will be very difficult to control.
© ABC 2014
17:37 EDT Much of western New South Wales has begun a heat wave, reaching at least five degrees above average for at least five days, averaging a maximum of 35 degrees or more.