Australia's hottest record average day has been broken again, with yesterday beating Tuesday's new record by a whole degree.

Temperatures reached an average of 41.9C on Wednesday. Tuesday, the record was set when temperatures averaged 40.9C.

The Bureau of Meteorology calculated the record by taking roughly 700 observations from weather stations across the country and placing them on a grid to calculate the average.

This heat map shows that Australia is the hottest place in the world right now. (Ventusky)

A ferry passes the Sydney Opera House as smoke haze from bushfires in New South Wales blankets the CBD in Sydney, Thursday, December 19, 2019. (AAP)

A global heatmap shows how bad the heatwave is, with Australia a completely different colour shade to all other parts of the world.

The record comes as states and territories suffer through astounding heatwaves in an already unbearable mass of bushfires and hazardous, smoke-filled air.

Air quality in Sydney is at hazardous levels again as fires continue to burn across the state, filling the air with a dangerous smoke haze.

Toxic bushfire smoke is plaguing most of NSW, with health authorities urge those with poor health and breathing difficulties to seek help if necessary.

Close to 100 fires are burning across the state today, pushing toxic plumes of smoke into heavily populated city areas. (AAP)

The heatwave scorched the city, which peaked at 39.3 degrees – the hottest December day in 15 years.

Penrith was the hottest suburb which reached 42.5 degrees.

The NSW Department of Environment says the haze has been the longest and most widespread event ever recorded as hundreds of people present to emergency rooms with respiratory issues.

At this stage no flights are affected by the smoke and ferries are still running on schedule.

Those driving are urged to be cautious on the roads with the poor visibility.

The quality of the air in Sydney's southwest this morning was 11 times worse than what is considered safe and the city's northwest was three times higher.

The smoke is due to almost 100 fires that have been burning across the state over the past weeks creating a hazardous environment for those daring to travel outdoors.

While winds today were too light to disperse the smoke out of the city, a gust this afternoon will push the smoke haze from the city out towards the Blue Mountains, but conditions will worsen when it returns on Saturday.

A gusty cooler change swept through about 4pm, which cooled much of Sydney by about 10 degrees.

"Aviation forecasts suggest that at times through the day visibility will drop to around 1,000m to 3,000m at Richmond Airport and 2,000m to 4,000m at times for Sydney Airport," weather specialist Graham Creed said.

SafeWork NSW executive director Andrew Gavrielatos said the heatwave brought significant risks to the health and safety of the public.

"Many people simply don't notice the symptoms of heat stress and by the time they are seriously impacted the ability to self-assess is compromised," he said.

"Employers must take heat stress seriously. Consult with your workers and take action to ensure workers are not exposed to heat stress."

Some Sydneysiders braved the heavy smoke to cool off outside in the heatwave conditions. (AAP)

The air quality in Sydney is toxic with conditions set to worsen on Saturday. (AAP)

"Aviation forecasts suggest that at times through the day visibility will drop to around 1,000m to 3,000m at Richmond Airport and 2,000m to 4,000m at times for Sydney Airport," weather specialist Graham Creed said.

SafeWork NSW executive director Andrew Gavrielatos said the heatwave brought significant risks to the health and safety of the public.

"Many people simply don't notice the symptoms of heat stress and by the time they are seriously impacted the ability to self-assess is compromised," he said.