SYDNEY, AUSTRALIA - Australia's Sydney Harbour was blanketed in a thick haze on Tuesday as a smoke cloud from controlled fires in the city's west swept across the central business district.

Health officials urged people to remain indoors after unexpected winds saw the smoke from the burning-off of dense bushland in the Blue Mountains, done as part of a fire hazard reduction plan, descend on the city.

'We do take weather into account and obviously that's a major part of planning a burn,' National Parks regional manager Geoff Luscombe told ABC Radio.

'Obviously we're going to have to look at ourselves afterwards and just work out whether or not we could have anticipated this better.'

A wind change is expected to see the haze dissipate overnight.