"Without a massive turnaround in policies, aside from the tragic loss of life and property, we will be asking firefighters to put themselves at an unacceptable risk," United Firefighters Union of Australia said in an open letter.

"We understand that our job is dangerous by its very nature. However, we are gravely concerned that current ... policies seem destined to ensure a repeat of the recent tragic events," said the union in an open letter to Prime Minister Kevin Rudd.

The call came as police detained two people on Thursday suspected of deliberately lighting one of the bushfires that savagely swept through southeast Australia on Saturday. 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. Prime minister Rudd has described the bushfires as "mass murder".

In Victoria, arson carries a jail term of two to 15 years, and 25 years if there's loss of life. The fires are the worst natural disaster in Australia in 110 years. The previous worst fires killed 75 people in 1983.

The firefighters union has now joined Green politicians and environmental activists in arguing that the deadly infernos are a climate change wake-up call to Australia.

Australia is one of the most vulnerable nations to climate change because of its hot, dry environment, but with its dependence on coal-fired power, Rudd has set a target to cut overall greenhouse gas emissions by only 5 percent by 2020.

In their letter to Rudd, the firefighters cited Australian scientists forecasting a "low global warming scenario" would see catastrophic fire events in Victoria every five to seven years by 2020, and by 2050, a doubling of extreme danger fire days. "Given the federal government's dismal greenhouse gas emissions cut of 5 percent, the science suggests we are well on the way to guaranteeing that somewhere in the country there will be an almost annual repeat of the recent disaster," they said.

Australia has launched its biggest arson investigation, "Operation Phoenix", into the nation's deadliest wildfires, believing at least one or more may have been deliberately lit. Fanned by strong winds and heatwave temperatures, several bushfires tore through rural towns north of Melbourne on Saturday night.

Melbourne's temperature on Saturday hit 46.4 degrees Celsius (115.5 degrees Fahrenheit), a record for the city. The disaster area, more than twice the size of London and encompassing more than 20 towns, has been declared a crime zone. The fires have burnt 1,033 homes and left 5,000 homeless. Standard & Poors says the damage could exceed $2 billion.

More than 4,000 firefighters are still battling some 21 fires in Victoria state, with several out of control. On Thursday, survivors returned to burnt-out towns and hamlets to rebuild their lives. Those with houses still standing offered shelter and support for those who lost their homes. But many were left to live in tents and caravans, having escaped the infernos with just the clothes on their backs.

"We have our health and we don't have to bury anyone, that's the main thing," said Chris King as she surveyed the rubble and twisted metal that once was her home.