A cool change that will end Victoria's hot spell will also create extreme bushfire danger, with forecast high winds and lightning strikes.
South Australia and much of Victoria sweltered on Sunday, with the mercury hitting 44.7C in Adelaide and 43C in parts of northwest Victoria.
A cool, southerly change bringing relief to South Australia on Sunday evening won't reach Victoria until Monday.
However, the change will bring with it high winds and lightning strikes without rain, creating severe fire danger.
Fire Services Commissioner Craig Lapsley said Monday was shaping as a major day of the fire season.
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"Victoria is very dry and ready to burn, as we have seen over the past two weeks," he said.
"This southerly wind change could pose a significant risk for fires that are currently being managed and any new fires that start."
With many students returning to school on Monday, Mr Lapsley urged families to have clear fire plans.
"Parents in areas of fire risk need to adjust their bushfire survival plans to include contingencies for school pick up on bad days like Monday," he said.
"They should also talk to a teacher about their school's bushfire plans."
Beachgoers trying to beat the heat at Lorne were given a scare when a two-metre shark was spotted within 300 metres of the shore.
Hundreds of swimmers were ordered out of the water for about 45 minutes on Sunday as surf lifesavers chased the shark away.
The hot weather also prompted the Victorian government to launch a timely reminder about the dangers of leaving children in hot cars.
The government launched the "no excuses, no exceptions" advertising campaign on Sunday after emergency services responded to 1100 cases of children being left in cars on hot days across Victoria in 2013.
