"We have a significant rain event on Victoria's doorstep," Bureau of Meteorology senior metrologist Kevin Parkin told reporters on Tuesday.
Mr Parkin said rain would likely peak on Thursday, along with wind gusts of up to 100km/h affecting elevated locations extending from the Grampians through to the Central Highlands including the Macedon ranges and alpine peaks in the state's northeast.
The BOM is expecting widespread falls of 20mm to 50mm across much Victoria.
"This event is probably the most significant rain event widespread across the state this year, certainly the most significant in recent months," Mr Parkin said.
Watch and act flood warnings have been issued for several rivers, with the SES urging Victorians not to camp near streams and rivers this weekend and to avoid driving to northern parts of the state.
"With the weather systems that we're about to see over the next 24 to 48 hours, we are asking Victorians to be flood ready," VICSES chief operations officer Tim Wiebusch said.
"In particular on Thursday, flash flooding is likely to be a risk in many parts of the state, including urban areas."
Victorian Premier Daniel Andrews said emergency services had hundreds of thousands of sandbags on standby and advised Victorians to be vigilant.
"We know that our catchments are full, we know that we've had record rainfall to this point, and the ground is absolutely sodden," Mr Andrews said.
"Please don't drive into flood waters, (it's) dangerous for you and dangerous for the people who will have to come and rescue you."
