A giant bushfire on the edge of Sydney, which has blanketed the city in smoke causing a spike in respiratory illnesses and the cancellation of outdoor sports, will take weeks to control but will not be extinguished without heavy rains, firefighters said.

Thousands of weary firefighters, who have been battling wildfires for a month, have been fighting nearly 100 blazes in New South Wales state.

The mega fire north of Sydney, Australia‘s largest city, was created on Friday when several fires merged and was now burning across 335,000 hectares.

“We need flooding rain to put these fires out. That’s really what is going to stop it,” said the New South Wales Rural Fire Service. “These will take many weeks to put out.”

Wildfires are common in Australia during the hot summer, which begins in December, but this year the fires started much earlier, blamed on soaring temperatures, dry winds and arson.

States of emergency declared as bushfires rage across Australia Show all 15 1 /15 States of emergency declared as bushfires rage across Australia States of emergency declared as bushfires rage across Australia A firefighter works on a bushfire believed to have been sparked by a lightning strike that has ravaged an area of over 2,000 hectares in northern New South Wales state AFP via Getty Images States of emergency declared as bushfires rage across Australia A dehydrated and injured Koala receives treatment at the Port Macquarie Koala Hospital AFP via Getty Images States of emergency declared as bushfires rage across Australia A water tanker airplane drops fire retardant on a bushfire in Harrington, New South Wales EPA States of emergency declared as bushfires rage across Australia Firefighters tackle a bushfire to save a home in Taree, 350km north of Sydney AFP via Getty Images States of emergency declared as bushfires rage across Australia A kangaroo is seen by the burnt remains of a vintage car in Torrington Getty Images States of emergency declared as bushfires rage across Australia Photo taken on November 9, 2019 shows bushfires taken from a plane in over north eastern New South Wales AFP via Getty Images States of emergency declared as bushfires rage across Australia Andrew Mackenzie surveys the damage around his home in Torrington Getty Images States of emergency declared as bushfires rage across Australia Fire and Rescue NSW firefighters conduct property protection as a bushfire burns close to homes on Railway Parade in Woodford NSW AP States of emergency declared as bushfires rage across Australia Australian Prime Minister Scott Morrison (L) comforts 85-year-old resident Owen Whalan at an evacauation centre in Taree 350km north of Sydney AFP via Getty Images States of emergency declared as bushfires rage across Australia Fire burns at Bolivia Hill in Glen Innes Getty Images States of emergency declared as bushfires rage across Australia A resident puts out small fires as he rides his motorcycle in Old Bar, New South Wales EPA States of emergency declared as bushfires rage across Australia A fire rages in Bobin, 350km north of Sydney on November 9, 2019, as firefighters try to contain dozens of out-of-control blazes AFP via Getty Images States of emergency declared as bushfires rage across Australia Construction workers speak as smoke haze drifts over Sydney, Australia EPA States of emergency declared as bushfires rage across Australia A vintage Jaguar car sits in ruins after a bushfire destroyed a property in Old Bar, 350km north of Sydney AFP via Getty Images States of emergency declared as bushfires rage across Australia A fire rages in Bobin, 350km north of Sydney AFP via Getty Images

A three-year drought has left much of Australia tinder dry.

The fires around Sydney have been pumping such vast amounts of smoke into the air that they appear as significant rain on the radars, the Bureau of Meteorology said on Twitter.

New South Wales Health said late on Friday that some 1,140 people had sought medical assistance for breathing issues or asthma in the past week – a quarter more than in a typical week. NSW Ambulance fielded about a third more calls.

Six people have been killed, nearly 700 houses burnt down and millions of hectares of land razed.

Strong winds fanned flames towards several suburbs in southwest Sydney on Saturday.

At least six people have been killed as the blaze rages on (AFP)

“It’s been going on all day, a fire came from the back and we put it out. But then another one came from the side so the fires covered the house in foam.,” said Luke Wright who helped save his brother’s home.

“The fence has been damaged but that’s about it, very lucky,” Mr Wright told local media.

Rural Fire Service Commissioner Shane Fitzsimmons said the worst might still be ahead, with temperatures forecast to rise into the 40 degrees in coming days and no meaningful rainfall expected until late January.

“It’s a tough couple of months ahead yet and we’ve already seen the horrific consequences of fire so far this season,” Mr Fitzsimmons told Australia’s 9News on Saturday.

Neighbouring Queensland state was battling some 45 wildfires and temperatures on Saturday as high as 40 Celsius.