A coalmine fire that could threaten Victoria's electricity supply is the priority for emergency services as they continue to battle blazes across the state.
The fire at Morwell, 130km east of Melbourne, is in the open-cut pit of the mine supplying the Hazelwood Power Station.
The escalation of the Morwell blaze came as Victoria's police chief commissioner Ken Lay revealed at least a dozen fires were suspected of being deliberately lit.
Victorian Fire Services Commissioner Craig Lapsley said the Morwell fire, which has destroyed several homes and is burning through logs and woodchip stockpiles at Australian Paper's Maryvale mill, is now his major concern.
"It is not threatening lives but it has the potential to impact on critical infrastructure for Victoria," Mr Lapsley said.
"It is not impacting on power generation in Victoria, but it has the potential to do so."
Two aircraft, fire trucks and the chief officers of both the Metropolitan Fire Brigade and the Country Fire Authority are at the blaze.
Mr Lapsley said putting out the fire would be complex because normal extraction of the coal was continuing and it was essential that no hot or burning coal found its way onto the conveyors supplying the power station.
"That will be a lengthy operation, and for those living in Morwell, a very uncomfortable operation because there will be black smoke over the town most of the time," he said.
"It's more than just a fire. It's about health issues within the town."
The Morwell fire took over as the state's most serious from the blaze that destroyed several homes on Sunday night as it spread from Mickleham, on Melbourne's northern outskirts, to Kilmore, 40km away.
It had burned more than 16,000 hectares by Monday evening.
The Morwell and Mickleham fires are among 200 fought at the height of the crisis on Sunday, 12 of which are believed to have been started by arsonists.
"There is sufficient evidence to suggest (the fires) are more than likely to have been deliberately lit," Mr Lay said.
He said some suspects had been identified.
None of the major fires are under suspicion, with Mr Lay reporting the most likely cause of the Mickleham fire is a tree branch falling across powerlines.
Mr Lapsley said more than 20 homes had been lost in the fires since Sunday morning, three of them in a built-up area at Warrandyte in Melbourne's northern suburbs, as well as those at Morwell and Kilmore.
Fires in Gippsland had burned out some 100,000 hectares, with a fire that burned 78,000 hectares in the Snowy River National Park causing serious concern.
The Morwell fire's impact on the community is limited and it isn't among those that were the subject of emergency warnings in place late on Monday.