Cool relief from Victoria's heat wave is on the way but authorities fear lightning strikes accompanying the change could spark more fires.
The warning comes as Melbourne endures another hot day, with the mercury tipped to hit 35 degrees and high fire danger in place across the state.
In the past 24 hours, firefighters have battled about 100 fires statewide, including three significant ones.
All fires are now under control but authorities fear lightning over the next 24 hours could start new blazes.
The northern Victorian region is facing a day of severe weather and very high fire danger with the temperature expected to hit 41 degrees in Echuca, 40 in Shepparton and 37 in Bendigo.
Fire Services Commissioner Craig Lapsley said a weather change would move through the state on Tuesday, with lightning storms that may spark fires.
"The fire services are at their full preparedness level and will continue through ... Tuesday, overnight and into early Wednesday to be very focused on what could occur in the state," he told reporters in Melbourne.
The Bureau of Meteorology is monitoring the storms, which are approaching the state's Mallee region from the north-west.
"With thunderstorms come lightning and there's always the risk that fires start," senior metrologist Kevin Parkyn said.
Further storms are expected to develop over western Victoria on Tuesday afternoon and across the state's eastern districts, including the southern foothills of the Grampians.
The storms may also hit Melbourne on Tuesday night.
Cool relief is expected to hit Melbourne and the rest of the state on Wednesday, with a milder week to follow.
Mr Parkyn said the searing heat over the past few days - which topped 40 degrees in Melbourne on Monday, 43 degrees in Dartmoor, 40 degrees in Swan Hill, 39 degrees in Yarrawonga and 38 degrees in the La Trobe Valley - is a sign of things to come.
"We're only really at the cusp of summer so it's highly likely we'll see more events like this," he said.
"We've never ever had a summer where I think we've had a 40 degree day every summer for 10 years in a row, and it looks like that's what's happened."
Acting premier Peter Ryan says it is critical people take heed of warnings from fire authorities.
He said the burning of a Country Fire Authority (CFA) tanker at Stonehaven on Geelong's outskirts on Monday, in which the crew of five escaped injury, showed the perils of fighting fire.
"Thankfully in this case their lives were spared, but it just goes to demonstrate when these incidents occur, people are exposed to literally life-threatening situations," he said.
Mr Ryan urged people, particularly holidaymakers staying in unfamiliar areas, to be aware of the fire threat and have a fire plan ready.
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