Wildfires have destroyed at least 59 homes in Perth, Australia's fourth largest city, where two major fires have burned for two days.

Fast and unpredictable flames swept through rugged terrain at Roleystone, on Perth's southern fringes, and along its northern outskirts at Red Hill, levelling 59 homes and scorching hundreds of hectares of forest.

A bridge over the Canning River collapsed in the flames and is likely to be impassable for at least three weeks.

Emergency chief Craig Hynes said there had been no serious injuries or fatalities. He said officials were prepared for the ‘remarkable’ winds, but he cautioned that authorities were yet to bring the fires under control.

Both are burning in areas of heavy vegetation on the city's outskirts, in rugged terrain that is difficult to access except by air.

‘We’re still calling both fires uncontrolled and we won't be able to let people back into the areas due to safety reasons,’ he said.

‘We are very concerned about the safety of the fire grounds and we are doing our best to make sure that there are no injuries. Life is our priority.’

The emergency comes exactly two years after the deadly ‘Black Saturday’ firestorm which claimed 173 lives in southeastern Victoria state, an anniversary marked Monday with memorial services in the worst-hit towns.

‘It’s a reminder to all of us just how long and painful the journey back from natural disaster can be,’ said Prime Minister Julia Gillard.

‘It is going to strike.... as perhaps a very cruel irony that on the day they mark the two-year anniversary of the Victorian bushfires so many Victorian communities are actually battling floodwaters,’ she added.