Police suspect nine of the state's bushfires in the past few days were deliberately lit.
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At least eight houses have been destroyed and more than 280,000 hectares burnt in more than 150 fires since the weekend. There were no deaths and the greatest property damage was at Gisborne, Mickleham and Warrandyte, on Melbourne's fringes.
Thousands of people have evacuated their homes, with 18 relief centres set up.
More than 6000 firefighters from as far as New Zealand are involved. The CFA said five firefighters had been injured, one of them seriously.
While temperatures have dropped from the weekend's high 30s to the mid 20s, strong winds and dry grassland continued to fuel the flames.
By late Monday afternoon, the Country Fire Authority said there were 20 out-of-control fires.
Police revealed that the arson squad was investigating the cause of 14 grass and scrub fires in the state and had judged nine to be suspicious.
They included blazes next to the Merri Creek at Fawkner in Melbourne's north; on the Great Ocean Road at Port Campbell; at Old Jindivick, in Drouin West, Gippsland, and at Havilah Road, in North Bendigo.
The causes of five other fires, including at Maiden Gully, Mornington and Gisborne South, had yet to be assessed.
Chief Commissioner Ken Lay said police had suspects for some of the fires. ''Some investigations are well progressed.
''We have a far far better picture than we ever have before on these people and how they behave.''
Police were revisiting the homes of known arsonists and patrolling high-risk areas.
But, he said, it was not only deliberately lit fires that were creating a headache for authorities.
''Fires have been lit by people simply not acting in a sensible matter by the way they use tools and other machinery.''
One of the most serious was the Mickleham fire that burnt 20,000 hectares in Melbourne's north. At 4.50pm the CFA issued an evacuation recommendation for the Bylands area south of Kilmore.
The CFA confirmed five houses had been destroyed by the Mickleham Road fires, not seven as previously estimated.
However, the full impact of the Mickleham-Kilmore fires was not yet known, as the CFA impact assessment teams had to pull out on Monday afternoon because of the increased fire activity.
The fire had headed north from Darraweit Guim towards Kilmore's southern and eastern edge including the McDougalls Road and Gehreys Lane area.
The CFA said residents in the area were in danger and should act to protect themselves. ''The safest option is to take shelter indoors immediately,'' the CFA website said.
Many people from the Kilmore area, some of whom survived Black Saturday, fled to a Red Cross-run shelter at Wallan, and were expected to stay the night.
In Gippsland, more than 20 fires were burning out of control.
Fire Services commissioner Craig Lapsley said the key fire on Monday was at Morwell, in the Latrobe Valley. ''The fire is burning currently in the Hazelwood open-cut mine and also at the Australian Paper Mill, at the northern side of Morwell,'' he said. ''It is not threatening lives but it certainly has the potential to impact on critical infrastructure for Victoria.''
Although the threat to many communities in the Gippsland region was downgraded early on Monday following a statewide cool change, some fires were expected to continue burning for days, and possibly weeks.
Authorities believe as many as three properties were lost in the Latrobe Valley on Sunday, but none were believed to be primary homes.
There have also been unconfirmed reports of properties lost in the remote settlement of Goongerah, near Orbost, in East Gippsland.
VicRoads reported 46 roads closed statewide, from Mickleham and Wallan to Numurkah, in northern Victoria, Dadswells Bridge near the Grampians and Morwell in Gippsland.
The federal and state governments said that victims of the bushfires would be eligible for government disaster assistance.
According to AAP, up to $500 for each adult and $250 a child will be offered to cover emergency accommodation, food, clothing or personal items and counselling.
Emergency re-establishment assistance of up to $31,050 a household is also available