SYDNEYSIDERS are set for a better sleep after the city sweltered through its warmest December night in almost 160 years.

A cool change has hit Sydney, with showers forecast for most of tonight, keeping it a coold 21C compared to last nights 27.1C.

Sydney has endured two scorching days in which in mercury reached the high 30s.

The mercury topped 37.2 today in the city and 38.2 in Richmond, which came after the hottest Sydney night in almost 150 years.

Camera Icon Kiah Nichols and Lucy Camden cooling off at The Entrance baths in extremely hot weather today. Credit: News Corp Australia, Sue Graham

Animal lovers across the state did all they could to keep their friends cool by hosing them down with some cold water.

The Bureau of Meteorology predicts a 60 per cent chance of rain when the fresh southerly comes.

Temperatures are set to drop to 22C tonight and continue into Thursday with a low of 19C, the weather bureau says.

Fireies had a tough day today as they battled as many as 51 fires across the state. The huge blaze in Abermain has been downgraded to a watch and act with no properties under immediate threat.

Increased winds near Neath have seen fire activity increase but there is no threat to homes as firefighters continue to battle the blaze throughout tonight. The fire at Patonga has been downgraded to Advice level but residents are asked to be cautious and monitor the conditions. There are still 19 blazes yet to be contained.

Camera Icon Kimberley Keegan 13 hoses down her hot horse "Lord Daniel "at Centennial parklands Equestrian centre at Moore Park. Credit: News Corp Australia, John Appleyard

Camera Icon Huge blaze in Neath which started yesterday. Credit: Supplied Camera Icon Fire fighters had a tough day battling the blaze. Credit: Supplied

Sydney struggled through the uncomfortably warm night on Tuesday, with temperatures in the city only dipping down to 27.1C, the highest minimum on record in 158 years since Christmas Day 1858, when they dropped to 26.3C.

Camera Icon A man showers after a swim in an ocean pool beside Bondi Beach today. Credit: AAP, AAP/Paul Miller

The temperature also smashed all but one previous record on Tuesday, making it the second-warmest Sydney evening in recorded history.

Water usage in greater Sydney also hit a record high on Tuesday, at 2171 megalitres, Sydney Water said.

“This is the equivalent of 868 Olympic sized swimming pools or 8.6 billion standard glasses of water,” spokesman Peter Hadfield said.

Total fire bans are still in place throughout greater Sydney, the Illawarra/Shoalhaven, lower and upper Central West regions, while there are severe fire danger warnings in Sydney and the Illawarra.

Camera Icon A graphic map of Australia highlights the summer temperatures setting in across the country. Credit: Supplied, Stormcast.com.au

On Tuesday the hot weather left Sydney, Canberra, Adelaide and Melbourne sweltering together for the first time in more than half a century.

Temperatures peaked above 33C in all four capital cities for the first time since 1965, according to the weather bureau.