Victoria's soaked northwestern towns are bracing for more heavy rain up to 40mm.
Light rain had begun by Tuesday evening, with Mildura recording about 4mm by 9:30pm, the Bureau of Meteorology said.
Heavy rain was set to develop in the evening, but by 9pm things were tracking slower than expected.
"It's still in a developing situation. I think it's probably going to be getting on closer to midnight when we start seeing some heavy rain up at the far northwest," senior forecaster Dean Stewart told AAP.
Incident management teams are on scene on Tuesday at towns surrounding the Avoca and Wimmera rivers which have been at major flood levels for more than a week.
Emergency management commissioner Craig Lapsley says the flooding threat is high with the amount of rain that has fallen in the past 10 days.
"The rivers are full, the reservoirs are full, the dams are full, so every drop of rain that falls from the sky is going to be in the river system and has the potential to increase flooding at that local level," he told reporters on Tuesday.
Heavy rain is expected to last for upwards of eight hours, with the bureau expecting rains to ease and move off to the northeast of the state by midday Wednesday.
The threat of more landslides along the Great Ocean Road is also being monitored.
Part of the road between the coastal holiday towns of Lorne and Wye River remain closed due to erosion.
"We've had water, mud, trees that have come onto the road and also as the water has travelled over the road. There has been some erosion," Mr Lapsley said.
There have been 21 people rescued from floodwaters across the state and a man has died in the past 10 days.