VICTORIANS should brace themselves for flash flooding and severe thunderstorms this afternoon.

The weather bureau said recent tropical humidity and a low pressure trough would trigger wild weather, starting in the Western District in the late morning, the Herald Sun reports.

Senior forecaster Scott Williams said the Grampians and the Wimmera would be among the first areas affected.

"It will extend across central parts of the state, including Melbourne, early in the afternoon before moving to Gippsland and the north in the late afternoon,’’ Mr Williams said.

"There is a small chance of 2cm hail stones and damaging winds. It is possible practically anywhere in the state.’’

The warnings come after the State Emergency Service said they received about 200 calls yesterday and overnight from areas west of Melbourne, including Melton and Bacchus Marsh, to deal with storm damage.

Yesterday a shopping centre's roof collapsed and a hospital cancelled elective surgery after the storm hit.

More than 75mm of rain fell in a band across Geelong, Ballarat, Bacchus Marsh and Melton, but failed to hit the CBD.

State Emergency Service spokesman Allan Briggs said staff had responded to 200 calls across the state, 80 of them at Bacchus Marsh and another 30 at Melton.

The Bacchus Marsh shopping centre in Main St was was evacuated after the wild weather caused the roof of a pet shop to partially collapse.