Media playback is unsupported on your device Media caption The BBC's Phil Mercer: "Strong gusty winds continue to push the flames to built-up areas"

Dozens of bushfires are sweeping across southern Australia, fanned by hot weather and strong winds.

Officials say an unknown number of homes have been destroyed and a firefighter has been injured in the state of Victoria.

Some residents have been ordered to leave and flames have spread to the outer suburbs of Australia's second biggest city, Melbourne.

Conditions in Victoria are at their worst since 2009, authorities said.

Then, wildfires killed 173 people and destroyed about 2,000 homes in a disaster dubbed Black Saturday.

At the scene Belle Nolan, Warrandyte, Victoria, Australia I live in Warrandyte in Victoria State with my fiance, Ryan - one of the worst affected areas. There's no co-ordinated evacuation, but we all have a bushfire emergency alert on our phones. We got an alert of a fast moving bushfire in the area, and were then told we had to evacuate. There was smoke, ash and embers everywhere. The police were already closing the roads. We got out just in time before another alert telling us it was now too late to leave. It's now 12 hours since we left and we're heading back. We have been told the fire is contained but not over, so we're not quite sure what we're going back to. We know that three houses have been destroyed and 25 acres of land destroyed. We do get a lot of alerts and some people are very complacent and say they will stay no matter what. But there is only one road out of town, so if there is a problem you do need to be on it.

Emergency crews are also fighting blazes in South Australia and New South Wales.

Cooler weather should help the massive firefighting effort, says the BBC's Phil Mercer in Sydney, although strong, gusty winds continue to fan the flames.

More than 70 fires are burning across Victoria and 15 emergency warnings are in effect, with up-to-date local information available on the Vic Emergency website.

Power station 'threat'

Hundreds of firefighters and dozens of fire engines are battling the blazes.

Fire authorities are worried about the threat posed to the coal-fired 1,600-megawatt Hazlewood Power Station in Latrobe Valley, local media reported.

Homes have been lost in the Melbourne suburbs of Warrandyte and Mickleham, and in Gisborne some 50km (30 miles) north-west of the city.

Victoria Premier Denis Napthine said help was available for anyone impacted by the wildfires.

"The Victorian government has an assistance package in place that will be rolled out immediately for those people who have lost their homes," Dr Napthine said.