Most of the regional Victorian centre of Castlemaine has lost power as the electricity supplier was forced to disconnect 9,800 customers due to the substation flooding.
It comes as residents of multiple Victorian communities in the state's north and central are being warned to prepare for major flooding as wild weather begins crossing Melbourne.
Electricity supplier Powercor said it was looking to bring generators to Castlemaine, north-west of Melbourne, after the substation began flooding, forcing the company to turn off power.
"We have taken this step to reduce the safety risk to emergency services and our employees and to minimise long term damage as much as possible in the circumstances," the company said in a statement.
It said about 2,600 customers were still connected, as their power could be supplied from a different part of the network.
Emergency services are advising people in Rochester, between Bendigo and Echuca, to evacuate as the Campaspe River continues to rise rapidly.
A relief centre has been set up at the Echuca United Netball Football Club on High Street. The river is expected to reach minor flood levels by 9pm this evening, and major flood levels by 10am Friday.
Residents in the towns of Carisbrook and Seymour were also advised to evacuate.
Authorities have issued emergency warnings for communities along the Goulburn and Campaspe Rivers as well as the Seven and Castle Creek catchments, predicting major flooding may occur in communities such as Seymour, Barnadown, Lake Eildon and Euroa within hours.
Flood levels at Seymour are predicted to reach levels similar to the May 1974 flood, which the SES said was the second-largest recorded flood in Seymour's history.
Flooding is expected to extend downstream on the Goulburn River to reach major flood levels at Shepparton by Saturday evening.
Authorities said a relief centre would be opened at the Seymour Sports and Aquatic Centre on Pollard Street.
It comes as thousands of homes across Victoria are without power and some regional townships are starting to be cut off due to floodwaters.
Heavy rain has also begun to hit Melbourne, with some parts of the city warned flash flooding could occur over the coming hours.
Emergency management commissioner Andrew Crisp said there was essentially a watch and act warning covering the whole of Victoria as the state soaked under heavy rain.
He said all Victorians, especially those in areas subject to emergency warnings such as Rochester, Barnadown, Seymour and Euroa, needed to listen to emergency services and evacuate if instructed.
"So what they need to do is what they have been doing up until now, is stay across their local conditions and respond, react to the messages that they are receiving," he said.
There are alerts across much of the state, with warnings ranging from advice to emergency levels.
Victorians are being urged to avoid all unnecessary travel for the next 24 hours.
The State Emergency Service (SES) has received thousands of calls for assistance already, and authorities have completed more than 30 rescues.
About 12,500 homes are without power across the state.
While rainfall is set to ease slightly tomorrow, SES chief operations officer Tim Wiebush said it was likely flooding would remain an issue in Victoria over the coming weeks.
"We're probably now looking at a period of 6-8 weeks that could exacerbate existing flooding," he said.
"Our water storages are absolutely full, our catchments are absolutely saturated, so every time we see reasonable rainfall, we're going to see some communities back under flood warnings again."
Roads and river warnings
Some regional townships are starting to be cut off as floodwaters close roads and access points.
Multiple roads have been closed, including the Melbourne-bound lanes of the Hume Freeway between Benalla and Avenel, the Western Highway in both directions at Great Western and the Calder Highway at Marong between Charlton and Wedderburn.
Major flood warnings remain in place across the state, with authorities warning the Thomson Dam in eastern Victoria could spill for the first time in 30 years.
The Thomson, Eildon and Dartmouth dams, which are already full, are expected to spill over the next few days.
In the 24 hours to 9am on Thursday, several towns were inundated with more than 100mm of rain with Strathbogie North (129mm), Charnwood (123mm) and Seymour (90mm) among the hardest-hit areas.
Deep potholes are being created by ongoing rain, with one truck driver telling ABC Central Victoria he encountered a pot hole "the length of a car" on the Hume Highway near Avenel, north of Seymour.
A warning has been issued for the Great Ocean Road at Separation Creek, where a landslide has affected one lane of the road.
V/Line has advised that the extreme weather has resulted in coaches replacing trains on multiple routes, such as the Shepparton, Albury, Echuca, Swan Hill and Warrnambool lines.
Some residents ready to 'stay and fight'
Multiple people have been rescued from floodwaters including a woman in Woodend, north-west of Melbourne, who became trapped in her vehicle.
"She got washed down to a bridge, but she's safe and well now," volunteer SES duty officer for the Loddon Mallee region Tracy White said.
"She has obviously driven into floodwater and her vehicle has floated down the road.
"She's managed to get herself sort of caught on the side of the bridge where crews were then able to extract her from the vehicle safely."
Earlier in the day, hundreds of residents in Rochester were banding together to prepare for the rising river levels.
The town is no stranger to floods, with about 200 houses — or roughly 80 per cent of the community — inundated with water in 2011.
Lindsay Vick's house survived the water 11 years ago and he said he had no plans to evacuate this year.
"I'm going to stay and fight it to the last man, I'm not going anywhere," Mr Vick said.
"Everyone's out and about, it's a great thing."
Mr Vick spoke to the ABC before the recommendation to evacuate was issued.
This morning holiday makers and residents in at the Rochester Caravan Park were moving to higher ground.
"We've only got three or four left in the park, some (are locals) waiting for their houses to be built," the park's manager Peter Willett said.
"We've only got five residents here. Most of those have found alternatives."
