A 71-year-old man has been arrested by Victoria Police in relation to a grass fire in Flowerdale, north of Melbourne, which started yesterday.
"He has been released pending further enquiries and the investigation remains ongoing," Victoria Police said in a statement.
"Police and CFA remain on scene and are currently working to keep the fire under control."
Anyone with information is urged to contact Crime Stoppers.
The fire continues to burn out of control and authorities say it's unlikely to be contained until tomorrow.
More than 700 hectares of land has been burnt near Spring Valley Road at Flowerdale after the fire broke out on Tuesday afternoon.
Emergency Management Victoria said it was one of the "most significant fires" they had seen this season.
About 100 firefighters are working on the blaze.
A Watch and Act alert remains in place for Dairy Creek, Flowerdale, Homewood, Kerrisdale, Strath Creek and Strath Creek along Upper King Parrot Creek Road.
CFA chief officer Jason Heffernan said conditions were constantly changing and the level of the alert could be upgraded.
"Residents in the warning area are advised to stay near shelter," he said.
"Residents need to keep up to date and monitor conditions and be ready to act."
Senior meteorologist Kevin Parkyn from the Bureau of Meteorology said Victoria was in the middle of a heatwave and a "real cool change" would not come until Saturday.
"Heat in combination with wind is what's going to be driving the elevated fire dangers over the next few days," he said.
"We've got high fire dangers Thursday, Friday, and Saturday, and it looks like we'll have extreme fire danger in the Wimmera on the Friday."
Emergency Management Commissioner Andrew Crisp said: "No-one can afford to be complacent anywhere in the state over the next few days."
Hopes fire will be extinguished by Thursday
Firefighters worked on the blaze through Tuesday night and were supported by water-bombing aircraft.
No homes have been lost and nobody has been injured, but fire authorities said the terrain was making work difficult for firefighters.
"We are making our way to try and contain this fire by 1700 or five o'clock tomorrow afternoon," said CFA incident controller Dave Bowden.
"We believe we'll have pretty conducive weather to do so today and also tonight. Probably less blustery winds than we had yesterday."
"Six large bulldozer machines to help us get a containment line around the fire," Mr Bowden said.
The CFA said the Whittlesea-Yea Road between Dairy Creek Road and Break O'Day Road is closed.
Murrindindi Shire councillor Sue Carpenter said she's confident lessons have been learnt from the Black Saturday bushfires and the fire won't threaten communities.
"We just keep our fingers crossed that things have improved since then with the authorities and that they're throwing so many people, trucks, aircraft at the fire," she told ABC Radio Melbourne.
"I just hope people can remain confident."
A Watch and Act alert has also been issued for a grassfire at Wildwood, near Sunbury, which is not yet under control.
