The Murray River is expected to reach major flood level in Echuca on Saturday, and emergency authorities say the river may now peak on Sunday or Monday.
State Emergency Service chief operations officer Tim Wiebusch said the estimated timing of the peak has been brought forward, after earlier predictions put the peak at Tuesday or Wednesday.
"The Murray River will reach the major flood level of 94.8 [metres] on Saturday," he said.
"It has now come forward a little bit from where it was yesterday from it being a peak of around 95 metres on Tuesday, to being overnight Sunday and through Monday."
Emergency authorities are also expecting flash flooding over the next 24-72 hours as storms emerge in parts of the state.
Michael Efron from the Bureau of Meteorology said rainfall totals of between 20 and 30 millimetres were likely later today, and some areas could get as much as 50 millimetres.
"We've already seen some thunderstorm development down across the south-west of the state. We're going to see that becoming more extensive as we come into the latter part of this afternoon and evening.
"Once those storms develop, they're not going to move much at all, so heavy rainfall leading to flash flooding is our main concern."
In Echuca, residents are on high alert as they brace for the impacts of the rising Murray River.
Authorities and the wider community have rallied to build a 2.5km-long flood levee in Echuca, but a local has said about 80 homes are on the wrong side.
Work underway to protect historic Cummeragunja site
When Carren Bux heard that the historic site of the Cummeragunja community was at risk of being flooded, she knew she had to help.
She travelled from her home in the New South Wales town of Deniliquin to the significant cultural site on the banks of the Murray River, to pitch in building flood barriers and sandbagging buildings.
"I've come over here to help my family, because most of my family is from over here. I've got sisters, and brother in laws and nieces and nephews that live over here," she said.
"Many families have lived here forever — there's a hell of a lot of history for a lot of the Cummeragunja fellas.
"If it was us in this situation we know that these fellas would be over helping their brothers and sisters."
Dozens of people from First Nations communities in and around the Cummeragunja community have been helping to protect the site, which is the homeland of some of the most significant First Nations leaders in Victorian and Australian history.
Three days ago, one of the flood levees around the site was breached.
Cummeragunja Land Council chief executive Leon Atkinson said the community had no supplies, and resources were being diverted to larger towns.
"That really broke our hearts," he said.
"I could see a lot of the anguish in other communities that are much bigger, much more highly populated."
On Wednesday, the community was overwhelmed by support, with people coming from far and wide, along with authorities to help protect the site.
"Someone sent a notice out via social media … we had this influx of uniforms and volunteers and we even had a helicopter drop a load of bags off. It was just so heartwarming," Mr Atkinson said.
He said the community had rebuilt levees to protect an old school building "loaded with history", and a medical clinic.
"It might just be two buildings, but the history can't be replaced," he said.
"To us it's important that we preserve it as it has been for hundreds of years. That's all we've got, we've only got this place."
Kerang isolated for at least a week
In the town of Kerang, about halfway between Echuca and Swan Hill, the Loddon River is expected to reach major flood levels as soon as today.
SES chief officer Tim Wiebusch said the Goulburn Valley Highway was now closed near Kerang.
"On the Loddon River, last night at Kerang we saw the plug effectively being put into the levee wall," he said.
"That now means that Kerang will be isolated for at least seven, if not more, days."
He said most of the community was expected to be protected by the levee, but 40 to 50 properties outside the levee could be impacted.
The floodwaters are not expected to impact the town's substation.
Many other Victorian communities are facing a challenging recovery following flood events, including the town of Rochester that only has a partially operational sewerage system.
