'Rare tornado' destroyed four Vic houses

The meteorological phenomenon that destroyed four homes in Victoria and damaged 60 others has been classified as a tornado.

An investigation was launched by the Bureau of Meteorology after severe storms wreaked havoc near Geelong on Wednesday.

The early findings are that a line of thunderstorms approaching Melbourne from the west quickly intensified to turn into a tornado that had winds of up to 160km/h.

"Really quite a violent wind gust came across a very short period of time in a very narrow corridor at night," Manager Weather Services Victoria Peter Otto said.

"It must have been terrifying for the poor residents."

Mr Otto said it wasn't strange for Victoria to have strong storms, but it was "very rare to get such a strong impact".

The four wrecked homes were deemed uninhabitable and the residents needed relocating.

The SES received 242 requests for help across the state on Wednesday.

As storms have moved across Victoria, Bureau of Meteorology Victoria State Manager Dr Andrew Tupper said flash flooding can affect bushfire-affected areas over the weekend.

"In East Gippsland we're expecting 20 to 14mm of rainfall, and in some areas up to 70mm," he told reporters.