23/09/2017 3:54 PM AEST | Updated 23/09/2017 7:09 PM AEST

Fire Closes Highway As NSW Swelters Under Record Temperatures

There are 70 bushfires in the state, and 20 are out of control.

An out-of-control bushfire is blazing in Sydney's South, briefly closing the main highway to the nation's capital as NSW experiences record breaking temperatures for the month of September.

The Hume Highway was been closed to all traffic on Saturday afternoon and an emergency warning was been issued for the Paddys River area near Wingello, while 70 bush and grass fires were alight by mid-afternoon, the NSW Rural Fire Service said.

The highway, which is the main highway between Sydney and Canberra, has been reopened in both directions.

Twenty of those fires are not contained, and a total fire ban has been declared for about half the state.

Temperatures soared past 40 degrees Celsius in some parts of the country, as Australia's east coast experiences a weekend heatwave.

The ABC reports firefighters and aircraft are working to slow the fire, with additional crews are headed to the area.

"We have sent out an emergency alert for those people in the direct impact of the fire run there, we have advised them that if you plan is to leave, now is the time to leave and make sure you only head in a northerly direction away from the fire front towards the Hume Highway," RFS spokesman James Morris told the national broadcaster.

Record September temperatures are in play across much of NSW, pushing the bushfire risks to "severe" in much of the state, and posing potential health risks for the elderly and those playing sport.

In Sydney, it's forecast to reach 33 degrees while in the west the mercury could hit a staggering 37 degrees.

The Bureau of Meteorology forecast yesterday, Friday, to be the warmest September day on record, and warned the extreme heat increased risk of bushfire—particularly in New South Wales and Queensland this weekend.

The high temperatures are likely to continue through Sunday, although conditions will begin to ease in western parts of New South Wales during Sunday, the BOM said.