Sydney (dpa) - Fire razed five houses on Melbourne's forest fringe Friday as residents of Australia's second-biggest city battled a record-breaking three consecutive days of above 43-degree heat.

The homes were lost in Boolarra North just hours before a cool change came through Melbourne and most of the state of Victoria and the temperature plunged to 28 degrees Celsius from 45 degrees Celsius.

"There's a lot of smoke, a lot of fire, a lot of people running around," a Country Fire Authority spokesman told Australia's AAP news agency. "We're continuing to work on asset protection."

Thousands of volunteer firefighters are battling the flames, backed by a fleet of water-bombing aircraft. More than 700 hectares of forest have been blackened.

Crews have been out in Melbourne hosing down rail tracks to stop more of them buckling. The intense heat has led to 310 rail services being cancelled.

More than 35,000 homes are without electricity because the power network can't cope with the demand for air-conditioning.

In Adelaide, where hospitals are struggling to cope with cases of heat stress, there was a fourth day of plus-43-degree heat.

But the searing temperatures of the southern hemisphere summer didn't stop 30,000 people from attending an outdoor rock concert. More than 120 volunteer medics were on hand and security personnel helped drench the revellers with high-pressure water hoses. (dpa)