Nearly 140 bushfires are raging in the Australian state of New South Wales, with the most severe burning in Sydney.

At their peak, there were seven separate fires in different areas of the city.

Firefighters battled them until the early hours of Friday morning local time.

Footage of one Sydney blaze shows firefighters running quickly away as the flames spread rapidly and suddenly.

Officials warned that many parts of the city would be blanketed with smoke.

At least four people have been killed and more than 400 homes have been destroyed since the fires broke out across Australia in early November.