Sydney hits hottest day on record

A fire burns in Ku-Ring-Gai National Park, north of Sydney.
A fire burns in Ku-Ring-Gai National Park, north of Sydney.
Firefighers battling a bushfire in Aberdare, New South Wales.
Firefighers battling a bushfire in Aberdare, New South Wales.
Frantic efforts to damp down properties as the fire approaches.
Frantic efforts to damp down properties as the fire approaches.
Trying to keep cool at the Big Day Out in Sydney.
Trying to keep cool at the Big Day Out in Sydney.
Swimmers and sun bathers at Victoria Park Pool, in Sydney's Glebe.
Swimmers and sun bathers at Victoria Park Pool, in Sydney's Glebe.
Crowds at Wanda Beach as temperatures begin to fall in Sydney.
Crowds at Wanda Beach as temperatures begin to fall in Sydney.
Sydneysiders cool off in Botany Bay near Yarra Bay.
Sydneysiders cool off in Botany Bay near Yarra Bay.
The changed landscape of Baradine Road at Coonabarabran, which was hit by one of New South Wales' worst bushfires in history.
The changed landscape of Baradine Road at Coonabarabran, which was hit by one of New South Wales' worst bushfires in history.
Robina and Felicity Otrupcek standing in front of Robina's home that was water-bombed and remained unscathed as fire burnt through the New South Wales property.
Robina and Felicity Otrupcek standing in front of Robina's home that was water-bombed and remained unscathed as fire burnt through the New South Wales property.
A children's playground destroyed by the massive bushfire in rural New South Wales.
A children's playground destroyed by the massive bushfire in rural New South Wales.
Fire burns alongside the Newell Highway near Coonabarabran, about 350km northwest of Sydney.
Fire burns alongside the Newell Highway near Coonabarabran, about 350km northwest of Sydney.
A fire danger sign on the Hume Highway between Sydney and Melbourne gives a grim warning to locals.
A fire danger sign on the Hume Highway between Sydney and Melbourne gives a grim warning to locals.
Several buildings at the Siding Spring Observatory were damaged.
Several buildings at the Siding Spring Observatory were damaged.
The Siding Spring Observatory the morning after the fire swept through.
The Siding Spring Observatory the morning after the fire swept through.
The fire moves in on the observatory in Siding Springs, in rural NSW.
The fire moves in on the observatory in Siding Springs, in rural NSW.
An aerial photo of the fire threatening the Siding Springs Observatory.
An aerial photo of the fire threatening the Siding Springs Observatory.
'Mopping-up" spot fires at Sandhills in Bungendore, Australia.
'Mopping-up" spot fires at Sandhills in Bungendore, Australia.
NSW Rural Fire Service crews water-bombing fires at Bungendore.
NSW Rural Fire Service crews water-bombing fires at Bungendore.
Carngham Station, in Victoria, was destroyed in the state's bushfires.
Carngham Station, in Victoria, was destroyed in the state's bushfires.
A fireman working on flames near Ballarat, Victoria.
A fireman working on flames near Ballarat, Victoria.
Fire crossing Princes Highway at Deans Gap fire in Shoalhaven, southern NSW.
Fire crossing Princes Highway at Deans Gap fire in Shoalhaven, southern NSW.
A deserted petrol station, close to a fire south west of Wandandian, NSW.
A deserted petrol station, close to a fire south west of Wandandian, NSW.
NSW Rural Fire Service crews tackle a deliberately lit bushfire near Bidwill in Sydney's west.
NSW Rural Fire Service crews tackle a deliberately lit bushfire near Bidwill in Sydney's west.
A bush fire burning near Cooma, south of Canberra.
A bush fire burning near Cooma, south of Canberra.
Smoke rises from the Yarrabin bushfire burning out of control near Cooma, south of Canberra.
Smoke rises from the Yarrabin bushfire burning out of control near Cooma, south of Canberra.
Water bombing at Oura, near Wagga Wagga. New South Wales faces its worst fire risk with temperatures predicted to hit the mid to high 40s.
Water bombing at Oura, near Wagga Wagga. New South Wales faces its worst fire risk with temperatures predicted to hit the mid to high 40s.
Rural Fire Service Commissioner Shane Fitzsimmons (C) at the State Operation Centre.
Rural Fire Service Commissioner Shane Fitzsimmons (C) at the State Operation Centre.
Exercise groups train at sunrise to beat the heat on Sydney's Bronte Beach as temperatures are expected to reach record highs.
Exercise groups train at sunrise to beat the heat on Sydney's Bronte Beach as temperatures are expected to reach record highs.
Singed clothes hang from a clothesline in a backyard affected by a bushfire at Boomer Bay, about 40 kilometres east of Hobart.
Singed clothes hang from a clothesline in a backyard affected by a bushfire at Boomer Bay, about 40 kilometres east of Hobart.
Kutchani, a female lion, eats a frozen milk iceblock at Sydney's Taronga Zoo.
Kutchani, a female lion, eats a frozen milk iceblock at Sydney's Taronga Zoo.
Police Rescue Helicopter crewman Matthew Drumm looks out at the destruction.
Police Rescue Helicopter crewman Matthew Drumm looks out at the destruction.
The settlement of Dunalley, about 40 kilometres east of Hobart, was one of the worst hit by the Tasmanian bush fires.
The settlement of Dunalley, about 40 kilometres east of Hobart, was one of the worst hit by the Tasmanian bush fires.
Fire burning near Dodges Ferry, a small town in south eastern Tasmania.
Fire burning near Dodges Ferry, a small town in south eastern Tasmania.
A fire at Tasmania's Forcett, 30km from Hobart, sends smoke over Park Beach.
A fire at Tasmania's Forcett, 30km from Hobart, sends smoke over Park Beach.

It was a tale of two cities for Sydney on Friday.

The city went from sweltering in record-breaking highs of over 45C to below-average temperatures in the space of about 10 minutes on Friday night.

And while the cool change wiped out the sizzle, it also brought severe thunderstorms and damaging winds that had residents battening down the hatches.

Wind gusts of up to 100km/h swept through the city as temperatures dropped by about 10 degrees in 10 minutes from about 8pm (AEDT), Bureau of Meteorology (BoM) forecaster Jake Phillips said.

"It went from the mid-30s to mid-20s in the space of five to 10 minutes in most areas," Mr Phillips told AAP.

The plummeting temperatures brought some relief to Sydneysiders after a sweltering day which saw the mercury hit a record-breaking 45.8C at Sydney's Observatory Hill at 2.55pm.

The previous record of 45.3C was set on January 14, 1939.

The sizzling heat caused chaos across the city, with scores of heat-related illnesses, transport meltdowns and even melting roads and ice rinks.

By 5pm (AEDT) on Friday, the Ambulance Service of NSW had responded to 93 cases of heat exposure.

On top of that, 133 people fainted and 37 people were treated for vomiting, with most of those cases attributed to the heat.

Sparks from Sydney's monorail briefly set fire to trees and grass near the entertainment centre, while at the Big Day Out music festival in Homebush a St Johns Ambulance spokesman said the organisation treated 200 people, mostly for dehydration.

In western Sydney at the Australia Youth Olympics, basketball, canoe and athletics events had to be cancelled or postponed because of the soaring temperatures.

Meanwhile, most trains across the CityRail network were delayed by at least an hour on Friday evening, with overhead wiring and signal problems failing to cope with the extreme heat.

It was so hot in Sydney's northwest that a 20km section of Bells Line of Road started to melt, with authorities cutting the speed limit to 60km/h because of safety fears.

And the manager of Canterbury ice rink, in Sydney's southwest, said it was so hot the ice inside the rink had been melting all day.

By 10pmhowever, Sydney was at a comfortable 23 degrees and the severe thunderstorm warning was removed.

The worst gusts were recorded at Terrey Hills in northern Sydney about 5pm on Friday, with gusts of 104km/h recorded.

The State Emergency Service (SES) received about 100 calls for help, mostly to do with falling trees and roof damage, a spokeswoman said.

The cool weather is expected to continue on Saturday, with forecast highs of 25 in the city and 28 in the west.

"That is actually below average for this time of year," Mr Phillips said.

"It will be a vastly different day from what we saw (on Friday), but after today I don't suppose too many people will be complaining."