UPDATE: ONE of the wildest storms of the year has lashed Victoria.

About 500 SES volunteers worked through the night trying to answer more than 800 calls for help, with houses unroofed, flash flooding, hail damage and trees blown over.

SES spokesman Lachlan Quick said that until 6.30pm yesterday the service had taken 150 calls from midnight but as the storm hit calls for help skyrocketed in the next two hours and reached just over 800.

"Most of those have related to flash flooding in the metropolitan area and the bulk of those have been in the Frankston bayside area," Mr Quick said.

There had also been about 200 reports of damage to buildings caused by hailstones and heavy rainfall.

There were 150 reports of fallen trees, many in in towns northwest of Melbourne including Castlemaine, Woodend and Maryborough, while in Wodonga a number of houses had their roofs ripped off, making two of them uninhabitable.

"We've got 53 units out working, around 400 to 500 volunteers, and I'd expect them to be going through the night," Mr Quick said.

Bureau of Meteorology senior forecaster James Taylor said at Oakleigh, in Melbourne's southeast, 12-14mm of rain and hail fell in just 10 minutes.

He said hail the size of golf balls hit Ballarat at the height of the storm.

"We also had a water spout reported off Black Rock (in Melbourne's bayside)," Mr Taylor said.

The rain was expected to persist in Melbourne until the early hours of Thursday morning, he said.

A Metropolitan Fire Brigade spokesman said crews were busy attending fire alarms set off by the wild weather.

Read more on the Herald Sun.