A record-breaking heatwave has gripped parts of southeast Australia, triggering catastrophic fire danger warnings and prompting dozens of school closures.

Unusually strong winds along the NSW south coast led to the highest fire warning level being called, with a total fire ban on Tuesday afternoon as 74 fires burned across the state.

Temperatures in Sydney soared past 34C as the harbour city faced record-breaking September heat.

Sydney Airport registered 35.9C just after 2pm, breaking the previous high of 35.6C set for the month in 2000.

The unseasonably hot and dry conditions are being felt across southern Australia, with temperatures peaking at 8-16C above average across much of South Australia, NSW and Victoria.

Miriam Bradbury from the Bureau of Meteorology said the prolonged run of days of high temperatures was particularly unusual. 

“This run of very, very warm weather hasn’t been seen for many, many years,” she said.

An approaching cold front is forecast to bring relief with considerable cooling for Victoria and Tasmania on Wednesday as the heat moves north into Queensland.

There’s no relief for NSW until Thursday, with many parts of the state, including Sydney, expected to reach 34C on Wednesday. 

Most of Australia will sit at moderate to high fire dangers for the next few days.

Fire crews have been busy in the NSW Hunter region and southeastern parts of Queensland, with up to 60 firefighters battling to control a blaze that burned about 176 hectares at Beerwah on the Sunshine Coast.

An emergency warning has been issued for an out-of-control bushfire on Tasmania’s east coast, with people in the Coles Bay Road area at Friendly Beaches advised to leave if safe to do so on Tuesday afternoon.

Greater Sydney was subject to the first total fire ban since late November 2020.

More than 3000 school children have been told to remain at home after the NSW Education Department listed 29 schools to close on the South Coast on Tuesday due to an elevated bushfire risk.

The fire ban and school closures apply across areas including the Bega Valley and Eurobodalla Shire.

RFS Commissioner Rob Rogers said Sydney and the Hunter region would experience the worst of the conditions on Wednesday before temperatures eased on Thursday.

“It’s the worst risk we’ve faced since the Black Summer fires of 2019,” he said.

“We’re in for a tough couple of days and we need the community to be very vigilant.”

The heat is expected to shift north later in the week into parts of Queensland, the Northern Territory and Western Australia, driving maximums to 40C.

A severe wind warning was in place for Tuesday in parts of the NSW Snowy Mountains and south west slopes, with strong gusts expected to become more damaging and widespread across the state on Wednesday ahead of a cold front.

The Australian Bureau of Meteorology declared an El Nino event on Tuesday afternoon, warning of hotter and drier conditions that could lead to severe heat waves, droughts and bushfires, particularly in the east. 

By Samantha Lock in Sydney