Sydney  - Police Tuesday began hunting arsonists behind the weekend's ferocious forest fires north of Melbourne as householders still in their path prepared to fight the flames or laid plans to flee them.

The death toll from Saturday's inferno reached 173, more than doubling the body count in Australia's previous worst forest fires in 1983.

Army bulldozers were out clearing the path for forensic teams to enter hamlets cut off by smouldering trees trunks and burned-out vehicles. Many were caught in their cars after leaving their escape too late, prompting fire chiefs to urge those near a fire to leave early or work up a plan to defend their property.

"People need to understand that a late departure is the most deadly," state chief fire officer Russell Rees said. "We've said, and it's clearly evident, fires can come without warning and very rapidly, and that you may not receive a warning and you may not have a fire truck at your front gate."

Officials who warned of a final tally above 200 said the likelihood was that not all victims would be identified.

Fires are still burning and Healesville resident Paul O'Dwyer said locals were leaving rather than staying to defend their properties.

"If it gets worse, they're gone," he told national broadcaster ABC. "So everyone is pulling back this time. No one really wants to stay and face it after what happened at Kinglake and that."

The popular mountain resorts of Kinglake and Marysville, 100 kilometres north-east of Melbourne, have barely any buildings left standing. Altogether at least 750 houses have been lost and 350,000 hectares of forest blackened.

Fire chiefs have rejected criticism that brigades were under-staffed and were caught by surprise. David McGay, a fire captain, said that some forest fires were too intense to tackle and that as many as 400 fires were raging on Saturday.

"But even if I'd had 20 strike teams all that would have happened is that we would have had 50 dead firefighters as well, me included," McGay said. "In hindsight, it's just as well I didn't have those teams because I would have deployed them."

The once quaint mountain resort of Marysville has been declared a crime scene because police believe the fire there was deliberately lit.

Experts say half of forest fires are the work of arsonists, who are seldom caught because their crime is so easy to commit and comes without an obvious motive to help police in their detective work.

Prime Minister Kevin Rudd described the work of arsonists as akin to "mass murder" and police in Victoria have deployed 100 detectives to catch them.

"Anyone who has seen anything, or has heard anything, we want them to come forward," Victoria Police Commissioner Christine Nixon said. "The firefighters themselves obviously watched fires that occurred and just don't believe that fires start those ways and could have occurred in that way."

Criminologist Damon Muller said boredom and attention-seeking were usually the motives behind setting forest fires and that less than 1 per cent of perpetrators are caught and prosecuted.

With fires expected to burn for weeks, brigades are being drafted in from around the country and even from abroad. New Zealand has 100 firefighters on stand-by to send and a team from the United States could be on the fire-ground later this week. (dpa)