Victoria has recorded its hottest November day with a small town in the state's north-west reaching close to 46 degrees.
The town of Ouyen has recorded a new record of 45.8 degrees.
It reached the soaring temperatures at about 3.00pm.
Earlier the Weather Bureau had reported a record of 45.5 degrees in Mildura.
It is the first time the state has passed 45 degrees in November since 1905 when the previous record of 45 degrees was set.
Weather Bureau senior forecaster Dean Stewart says it is unusual the November record has stood for more than a century.
"The fact that it's lasted so long might be more surprising," he said.
"In these days when we seem to have an increased number of hot days, I guess for a record to last that long is a little surprising, but it had to be passed at some stage and today's the day."
Mr Stewart says the heat has been building up inland over the last few weeks.
"Mildura's now had a run of days, five successive days before today, above 35 degrees and to top it off with a day of 45 is fairly unusual," he said.
"Of course reaching 45.4's obviously never happened before , so I guess you could say unprecedented heat over the north west of the state."
As the state endured its hottest spring day on record, firefighters have been battling a number of grassfires, including a fast-moving one that has burnt through 100 hectares in central Victoria.
Two fire-fighting aircraft are helping to attack the fire which broke out near the town of Baringhup, between Maryborough and Castlemaine, just after 3.00pm.
The Country Fire Authority (CFA) has issued a 'watch and act' alert for residents of Baringhup, Baringhup West, Carisbrook, Joyces Creek and Moolort.
Duty officer Brett Boatman says other fires at Dartmoor and Edenhope in the state's west and near Talbot, also in central Victoria, have been contained.
"It's hot and reasonably windy through the central part of Victoria and in that area, the fuels up there are fairly dry," he said.
"We are expecting a wind change to move through the state, but not until later in the evening which will bring cooler conditions, but yes, the weather conditions certainly aren't helping."
Ambulance Victoria says it has received eight reports of children being left unattended in cars.
Operations manager Paul Holman says it only takes a couple of minutes for a child to die in a hot vehicle.
Commuters are also being warned to expect delays leaving the city this afternoon.
VLine says it's imposed a heat speed restriction, which is expected to add about 20 minutes to most journeys.
And Metro has replaced services on the Upfield line with buses, because of problems with the tracks.
The Bureau of Meteorology says a cool change, courtesy of a thunderstorm, is expected after midnight, and tomorrow in Melbourne is likely to be 26 degrees, with patchy rain.
© ABC 2012
14:24 EDT Thunderstorms are due to develop daily across New South Wales and Queensland for almost two weeks.