Melbourne has recorded its hottest day since records were first kept in the 1850s, when the temperature reached 46.4 just after 3pm.
Saturday's heat smashed the previous record of 45.6 degrees Celsius set on January 13, 1939 - known as Black Friday.
Bureau of Meteorology senior forecaster Stuart Coombs said the highest recording was at Avalon, southwest of Melbourne which topped 47.9C at 2.50pm.
Visibility was also reduced as dust storms were whipped up by strong winds.
Coombs said visibility was down to 1,000 metres at Swan Hill in the state's northwest.
He said the squally west-southwesterly winds that are accompanying the cooler change would not bring any relief to the state's firefighters, who are battling six major blazes.
"The change won't help the firefighters," Coombs said.
"The fires that have burnt southeastwards through the day, all of a sudden the left hand flank of all those fires is going to become the front and that will cause all manner of problems."
The heat has also severely disrupted Melbourne's suburban train system and Victoria's rural train services.
Connex spokesman John Rees said that up until 3pm (AEDT) 60 suburban trains had been cancelled and that number was expected to climb.
He said train lines at Williamstown, Glen Waverley and Alamein had been shut down and replaced with buses until further notice.
A V/Line spokesman said three of its five train services in regional Victoria have been shut down in Gippsland, Seymour and Warrnambool.
He said it was difficult to estimate when the services would be back up and running as they were not yet able to get to the affected areas to assess any damage to train lines and infrastructure.
About 95 residents in two nursing homes at Neerim South and Bunyip were relocated to the Warrigal and Koo Wee Rup hospitals in a precautionary measure against the bushfires in those regions.
Powercor spokesman Hugo Armstrong said 20,000 customers were left without power in the Wimmera due to branches being blown onto power lines or because of the high demand on the service.
The bushfire at Horsham has also left several thousand customers without power.
"We are unable to get into the area to assess the damage because of the fire," Armstrong told AAP.