Sydney - Melbourne residents turned on authorities Saturday after enduring four days of record heat that knocked out power lines, sidelined commuter train services and stoked forest fires that have claimed at least 20 houses on the fringes of Australia's second-biggest city.

"It's an extraordinary situation, and Victorians have every right to be angry," opposition Liberal Party leader Ted Baillieu said in response to the tirade of criticism.

Train tracks - and the state's electricity grid - buckled in a record-breaking spell of three consecutive days of above 43-degree temperatures.

More than half a million homes were left without power, hundreds of train services were cancelled and motorists were stranded by inoperative traffic lights.

Resources Minister Peter Batchelor urged calm and understanding as workers struggled to keep essential services running.

"These events are unprecedented," he said. "In some respects, they are not unlike a natural disaster impacting on a community like a flood or tornado. No government or system can withstand that sort of attack on it without there being some problems."

The 20 homes lost were in Boolarra North. Volunteer firefighters aboard more than 100 fire engines were battling the flames, backed by a fleet of water-bombing aircraft.

About 5,000 hectares of forest in the state of Victoria have been blackened. Officials warned of worse trouble ahead if the flames reach high-voltage cables.

"Our major concern at the moment is whether or not the fire encroaches on some of the transmission lines and, therefore, has perhaps some impact on our ability to keep generation going to the grid," said Loy Yang Power chief executive Ian Nethercote.

Baillieu said the likelihood was that the fires were the work of arsonists taking advantage of perfect conditions to lay blazes.

"If these bushfires were deliberately lit, then whoever has done this deserves to have the book thrown at them," he told reporters. "We need a register of arsonists in this country, and we need mandatory minimum sentences for people found to have deliberately lit bushfires."

Penny Wong, climate change minister in the federal government, linked the heat wave to global warming.

"Eleven of the hottest years in history have been in the last 12, and we also note, particularly in the southern part of Australia, we're seeing less rainfall," she said. "All of this is consistent with climate change, and all of this is consistent with what scientists told us would happen." (dpa)