Victoria is bracing itself for the heaviest rainfall in nearly 15 years, with rainfalls of up to 150mm predicted to fall in the northeast of the state.

The rain started in Ballarat about 8pm last night and three hours later, 6mm had been dumped.

Heavy and intermittent rain was predicted for much of the night.

Residents can expect between 25mm and 50mm of rainfall this weekend, depending on the location.

Bureau of Meteorology senior forecaster Dean Stewart last night predicted rain for 18 hours across the city, but with breaks in between.

''It may not be constant but there will be rain over the next 18 hours. There will be periods where it will be heavy at times,'' Mr Stewart said.

''At times the rain could potentially be heavy so there could be some flash flooding around the Ballarat region.''

Destructive winds averaging 60 to 75km/h with widespread peak gusts reaching 130km/h were forecast to develop last night in the region.

Mr Stewart said the Ballarat area was on flood watch, with severe weather warnings issued for the strong winds expected today.

''At times the rain could potentially be heavy so there could be some flash flooding around the Ballarat region,'' he said.

Victoria State Emergency Service regional duty officer for the mid west region Tony Grimme said that despite flood concerns, most of Ballarat drained well.

''But outside the city there could be flooding on the low-lying area which could hold water,'' Mr Grimme said.

Victoria Police warned motorists to be careful in the wet conditions, particularly those driving in to the snow this weekend.

''There is potential for widespread flooding, and drivers should be careful if driving close to the roadside edges as the excess water may cause some unsealed roads to become soft, slippery and slightly unstable,'' Superintendent Alan Byrnes said.

EnergySafe Victoria urged householders to prepare for power outages when wild weather hits.

It advised residents to have a torch ready, a charged phone that doesn't rely on electricity to operate, such as a mobile, and access to important contact numbers, including the faults number of their local power distributor.