Up to 20 towns in addition to those already flooded or under threat are expected to be hit by floodwaters in coming days, and tens of thousands of Victorians face the prospect of no electricity.
More than 3500 people have been hit by the historic floods, while 1600 properties have been affected in 46 towns. Emergency services have received more than 5000 requests for help.
The floods may have claimed their first victim when a seven-year-old boy disappeared on Monday while swimming in a billabong off the moderately swollen Goulburn River near Shepparton in the state's north.
While the town of Horsham was bracing for a "one-in-200-year" flood to hit on Monday night, Premier Ted Baillieu warned the crisis is not over yet.
Flooding is expected to continue in some areas of the north and northwest, including Kerang near the NSW-Victorian border, for up to a fortnight.
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State Emergency Service Controller Tim Wiebusch urged communities in the Avoca, Loddon and Wimmera catchments to stay alert, as canals and streams that are not part of the major river systems are experiencing unprecedented flows.
Communities that could be hit include Dingwall, Appin, Terrick Terrick and Rowlands southeast of Kerang and other towns north of Bridgewater on the Loddon River and north of Charlton on the Avoca.
Mr Wiebusch said many more towns would battle floodwaters in coming days.
"We are still to see in the order of perhaps 10 to 20 other communities that will still see effects of flooding over coming days and still see some of these flood peaks to come," he told reporters in Melbourne on Monday.
"We are appealing to people in all of those areas to stay very much alert to their conditions so that they can act if we have information at hand to alert them.
"In all cases we may not have the information at hand because some of those systems, canals and the like, do not have gauges."
Mr Wiebusch said the Wimmera River was expected to peak at Horsham late Monday into early Tuesday, splitting the town in two and closing the Western Highway. In coming days flooding was also expected at Warracknabeal, Dimboola and Jeparit, north of Horsham.
Mr Baillieu said authorities were confident the power sub-station in Horsham had been secured, while work to build a second levee at the station in Kerang was under way.
About 20,000 people could be without electricity if floodwaters breach the levee at the Kerang sub-station.
Mr Wiebusch described the imminent flood in Horsham as a one-in-200 year event and the expected flood at Kerang as one-in-100 years. He said more than 100 people, including those in cars, have had to be rescued from floodwaters across the state in the past week.
Victoria Police Assistant Commissioner Stephen Fontana warned people caught swimming or riding boats in flood-affected areas face a fine of $191 and criminal charges.
Horsham Mayor Michael Ryan said the flood was especially disappointing following years of drought and flooding in September. "Nothing surprises anymore.
The water has wrecked farms, wrecked crops and that's the irony of it all," he said. "We hoped for rain and now we wish it would go away."
The Campaspe River peaked in Echuca late on Sunday, but did not breach the levee bank.
Prime Minister Julia Gillard visited Echuca on Monday and urged the insurance industry to show the same generosity of spirit the Australian people have shown throughout the floods crisis.
Mr Baillieu said about 80 to 100 homes were affected in Echuca, with only a few being inundated.
He said the state government had requested financial assistance from the Commonwealth and he was confident the money would be provided.
