At least 10 homes have been destroyed in Sydney in a terrifying start to Australia's annual bushfire season.

Firefighters are battling more than 70 fires in New South Wales, 47 of which are around Sydney.

Some of the fires may have been deliberately lit, fire officials said.

Last year, more than 100 homes were destroyed and at least 500,000 hectares (1.2 million acres) of land in the state were consumed by Australia's longest ever bushfire crisis.

More than 100 residents were evacuated on Tuesday in the southern Sydney suburbs of Engadine and in the Windsor Downs area, which lies to the west of the city close to the Blue Mountains national park.

There are no reports of injuries but a number of firefighters have been treated for smoke inhalation.

Unusual weather

Temperatures in western Sydney were around 30 degrees Celsius (86 Fahrenheit) and the flames were being fanned by strong winds and near record low humidity.

Such conditions were unseasonal, and a "pretty good indication of what is to come for the next three to four months," said Rural Fire Service commissioner Phil Koperburg.

But fire service spokesman Cameron Wade noted that, since there had been no recent lightning strikes in Sydney, "we have got to put these fires down to human intervention of some sort, be it accidental or deliberate".

Officials say more than half of last year's fires were deliberately lit, many by bored teenagers.