Sydney - Residents of Australia's biggest city woke up Saturday to the smell of smoke from forests set ablaze by arsonists making the most of the tinder-box conditions plaguing Sydney and other south-coast cities.

The fire in a national park north of the harbour city is just one of dozens in the south-east corner of the continent powered by record temperatures and strong winds.

Sydney is set to break an all-time record of three consecutive days of plus-40-degree-Celsius heat.

"Potentially we are looking at the worst days we've seen this season," said Rural Fire Service spokesman Ben Shepherd, noting that all of the 70,000 volunteer firefighters in New South Wales were on standby.

To thwart arsonists - half of forest fires are believed to be deliberately lit - authorities have closed some national parks.

In what may have been a first, a court last week refused a volunteer fireman bail because of fears he would re-offend. He had been charged with setting forest fires and was awaiting trial.

In Melbourne, around 1,000 kilometres down the coast from Sydney, a fire on a forest fringe was threatening power lines to the nation's second-biggest city and state capital.

State Premier John Brumby said the state of Victoria faced its worst-ever bushfire threat.

"We're going to have unbelievably high temperatures and we're also going to have unbelievably high winds," Brumby said. "We've got a state which is just tinder dry."

Melbourne recorded is hottest February day, with the temperature above 44 degrees Celsius, and Brumby warned of a possible repeat of the blazes in 1983 that left 75 people dead.

In Adelaide, the South Australia state capital, the temperature was already 37 degrees at breakfast time and 10,000 volunteer firefighters were being marshaled to tackle forest blazes. One of the state's 11 water-bombing aircraft has already been in action. (dpa)