MELBOURNE (REUTERS) - A giant blaze that has blanketed Sydney, Australia's largest city, in a hazardous smoke could take many weeks to put out, fire services said late on Friday (Dec 6), with the whole region fighting nearly 100 fires and expectations that the worst is yet to come.

While common in Australia during the hot summer, which begins in December, bushfires have begun much earlier this season, blamed on soaring temperatures, dry winds and suspected arson.

The most recent blaze north of Sydney, burning across 335,000ha, has caused the cancellation of many outdoor weekend activities as smoke and ash have lingered over the city.

"These will take many weeks to put out - and only when we get good rain," the New South Wales Rural Fire Service said in a statement late on Friday.

Wildfires have killed at least four people and destroyed more than 680 homes across eastern Australia, according to the authorities.

Although the heat and wind eased a bit on Saturday near Sydney, RFS Commissioner Shane Fitzsimmons told Australia's Sky News television that it was going to be "another tough day for everybody involved".

Some 2,000 firefighters have been deployed to fight 96 fires throughout the state, whose landscape has been parched by three years of drought. Only about half of the fires were contained.

"People are nervous and they have a right to be," Phil Koperberg, founder of the Rural Fire Service, said, according to The Sydney Herald Morning. He warned that with the forecast calling for more dry conditions and more heat, "the worst is yet to come".