The State Emergency Service (SES) says it received 250 calls for help within one hour from residents at Ballarat, about four calls per minute, from 9pm (AEDT) as the storm hit on Friday night.
SES spokesman Lachlan Quick said the calls, mostly from the suburbs of Sebastopol, Mount Helen and Mount Clear, were still coming in on Saturday morning, bringing the total number of calls to 330.
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He said the calls for help concerned building damage from heavy wind, rain, hail and fallen trees, as well as trees fallen onto roads.
"People have woken up and discovered more damage to their homes," he said.
Mr Quick said SES volunteers from neighbouring units as well as Melbourne and Geelong had been called in to help clear the backlog of calls.
There were still about 120 people waiting for assistance, many with damage to their roofs, he said.
"We expect it will take all of today and potentially some of tomorrow to clear it all up," he said.
"They are certainly not 15 minute jobs, many of them will take several hours."
The storm left 9000 homes in the state's southwest without power.
Gordon Badham, spokesman for electricity distributor Powercor, said while power had been restored to the majority of residents, crews were still working to reconnect 2500 homes in suburbs around Ballarat.
Another 500 homes in Geelong, Warrnambool, Colac and Ararat were also without power on Saturday morning, he said.
"We've had downed lines and trees across lines, we've had trees blocking roads and other obstructions, so it has been complicated," he said.
"(The storm) was short and sharp but it certainly produced some serious impact."
Mr Badham said power was expected to be restored to all homes on Saturday afternoon.
Bureau of Meteorology senior forecaster James Taylor said severe thunderstorms were forecast to hit the state's east later in the afternoon.
