Victoria has recorded its hottest November day, at 45.4 degrees in Mildura this afternoon.
It is the first time the state has passed 45 degrees in November since 1905, when the previous record of 45.0 was set, also in the state's north west.
Weather Bureau senior forecaster Dean 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 of course for this time of year," he said.
"Reaching 45.4's obviously never happened before, so I guess you could say unprecedented heat over the north west of the state.
Earlier firefighters contained a number of small grass fires including a fire near Locksley, which had 13 fire trucks on site.
The says hot northerly winds and humidity of around ten per cent will create severe fire conditions in the west of the state.
The Country Fire Authority (CFA) has placed extra aircraft in the north-west of the state as a precaution.
CFA spokesman Brett Boatman is asking farmers in the west and the north-west to delay harvesting until the danger passes.
"We're saying to harvesters and contractors if they can delay their works until the fire danger passes, that reduces the ignition and the chance of fires," he said.
Paramedic Brett Drummond is urging people drink plenty of water, avoid alcohol and caffeine and be aware of signs of dehydration.
"Symptoms sometimes can be fairly mild dizziness to feeling faint," he said.
"Then they can progress to being more severe. That might include cramps, feeling dizzy and confused it can even lead to unconsciousness."
The hot weather is also expected to cause delays on V/Line train services. Speed restrictions will be introduced between noon and 8:00pm (AEDT).
V/line says services this afternoon could be up to 30 minutes slower and may be replaced by buses.
As temperatures rose in Melbourne, the elephants at Melbourne Zoo took to the water.
All three elephant paddocks have pools, one of which is four metres deep.
The zoo's two calves, Mali and Ongard, are good swimmers and enjoyed a dip in the deep pool today, chasing after floating frozen fruit.
Swimming lessons are part of the exercise program designed to keep the elephants happy and healthy.
© ABC 2012
12:51 EDT Melbourne is about to cool off this afternoon before 40-degree heat spreads across southern Australia late in the week.