The bushfire that raged through Dereel in western Victoria on Thursday, although fanned by the continuing dry hot summer, may have been intentionally staged up, according to arson detectives.

Arson detectives still have yet to gather credible evidence, but they found the bushfire highly suspicious especially since it burned mostly private lands, including a farmland and scrub country.

"Arson is absolutely disgraceful behaviour, unacceptable behaviour, to put lives at risk, put properties at risk," Denis Napthine, Victorian premier, said at the scene after being briefed on the bushfire and initial theories.

"We will leave no stone unturned to make sure we reduce the risk of arson in Victoria."

The Dereel fire is believed to have damaged less than 10 buildings. Residents are not allowed yet to return back in as arson investigators do their job, according to Gerry Verdoorn, CFA district operations manager.

Others believed it damaged up to 12 properties across 1,300 hectares.

"We're hoping as soon as possible we can let the locals back in there," he said.

The blaze, which started 11:30am on Thursday, was for some 45 minutes transformed into a catastrophic code red category, the state's highest fire alert.

"It was a pretty dynamic environment," Craig Lapsley, Fire Services Commissioner, told the Nine Network. "The intensity was significant."

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Raging Victorian Bushfires Claim Homes, Properties