Parts of Victoria have had a month of rain in less than a day, with emergency workers called to rescue two people from flash floods.
The Bureau of Meteorology's Dean Narramore says it's been the wettest day for a year.
"Victoria has copped a drenching in the last 24 hours," he said
"Many locations, not only in Melbourne but right across western and central Victoria, have had a month's worth of rain in less than six-to-12 hours," he said.
The State Emergency Service has rescued a driver from a vehicle trapped in floodwaters in South Melbourne, and another from a vehicle in Bendigo.
Almost 100 SES units have responded to more than 600 calls for help in the past 24 hours, the majority for leaking roofs and other flood damage.
SES operations manager Josh Gamble is warning residents in flood-prone areas to monitor the conditions, and either leave the area early, or be ready with sandbags should the waters rise.
"We know flash flooding comes up out of nowhere, so we can't plan for where it may impact," he said.
Flood watches are in place for the north central catchments, from the Avoca River to Broken River.
There is also a minor flood warning for the Yarra, and the EPA is warning people to avoid contact with the river at Warrandyte, Kew, Healesville and Launching Place.
Water quality warnings are also in place for 36 beaches around Port Phillip Bay.
Melbourne, which has a January average rainfall of 47mm, has copped 43mm of rain since 9am on Friday.
In the suburbs, Heathmont and Viewbank both saw 51mm, while Melbourne airport received 51mm.
The town of Pyalong, north of the city, had 75mm, while Mt Buffalo also experienced heavy falls with 71mm.
Mr Narramore says conditions may not ease until early to mid-morning on Saturday.
"Flooding and flash flooding is definitely going to become an issue in the coming days and weeks," he says.
More storms are predicted for eastern Victoria on Friday night.