Australian police have detained two people suspected of deliberately lighting one of the bushfires that have swept through southeast Australia killing at least 181 people and leaving 5,000 homeless.

'The investigation is in its initial stages. Two people are assisting police with inquiries,' a police spokeswoman said today. Police would not give further details.

Prime Minister Kevin Rudd has described the fires as mass murder.

Authorities say the toll is expected to rise beyond 200 as more bodies are discovered in the charred remains of houses in the southern state of Victoria.

One razed town, Marysville, sealed off to the public due to the horrific scenes there, may contain 50 to 100 more dead, authorities say. That would bring the toll to around 300.

In Victoria, arson carries a jail term of two to 15 years, and 25 years if there is loss of life.

Several bushfires tore through rural towns north of Melbourne on Saturday night, fanned by strong winds and heatwave temperatures. Melbourne's temperature on Saturday hit a record 46.4 degrees Celsius (115.5 degrees Fahrenheit).

The disaster area, encompassing more than 20 towns north of Melbourne, has been declared a crime zone. The fires have burned 1,033 homes and left 5,000 people homeless.

Standard & Poors estimated the damage could exceed $2bn (€1.01bn).

Survivors are beginning to return to their burned-out towns and those with houses still standing have offered shelter and support.

But many have been left to live in tents and caravans, having escaped the infernos with just the clothes on their backs.

Australia has launched Operation Phoenix, which is its biggest arson investigation.

'We're sure that the fire in Churchill...was deliberately lit and we have now been given some information that makes us suspicious about the Marysville fire,' Victoria Police Commissioner Christine Nixon told local television.

'We're obviously working very hard on that investigation, and we've spoken to a number of suspects so far, but it's still an ongoing investigation. We'll get there, but it is a matter of piecing together all of the evidence,' she added.

More than 4,000 firefighters are still battling some 21 fires in Victoria state, with several still out of control.

Ms Nixon said police had received reports that more fires had been deliberately lit since Saturday.

'We certainly have had reports of other fires being lit,' Ms Nixon said. 'You and I would just be staggered by that, but that's what we're certainly seeing.'

The tragedy is the worst natural disaster in Australia in 110 years. The previous worst bushfire was the Ash Wednesday fires of 1983, which killed 75 people.