Sydney has officially recorded its hottest day on record, with the mercury reaching 45.8 degrees at Observatory Hill.
The searing temperature equates to about 114 degrees on the old Fahrenheit scale.
The previous record was 45.3 degrees in January 1939.
Across greater Sydney, the hottest temperature recorded so far has been at Camden which reached 46.4 degrees shortly after 3:00pm, but that is still short of the record for the western suburbs.
Aaron Coutts-Smith from the Weather Bureau says other records could still be broken.
"We're keeping a very close eye on it," he said.
"They can still continue to rise this afternoon, it's really contingent on the sea breeze and when that decides to kick in and move further inland."
Grass fires have been springing up around Sydney areas as temperatures soar across the city.
A grass fire in the rail corridor at Kingsgrove has lead to trains bypassing stations on the Airport and East Hills line in Sydney's south.
New South Wales Fire and Rescue crews have also put out fires in parks in Yennora in the south-west and Penrith in the west.
Paramedics feel the heat
The New South Wales Ambulance Service has been flooded with calls for people seeking help for heat exposure.
At least 21 people have called the ambulance service seeking help for heat exposure.
A further 84 calls have been received for unconsciousness, fainting and vomiting which the Ambulance Service says can also be attributed to heat stress.
In the last ten days 182 people called on paramedics seeking emergency treatment for heat stress.
Chief Superintendent Ian Johns says that figure is just the tip of the iceberg.
"We get hundreds more calls for people complaining of heat related illness," he said.
"People call 000 for dizziness or vomiting or headache or generally unwell or collapse, and when the paramedics get there and do some assessment it can be attributed to the excessive heat.
"People underestimate the heat and overestimate their ability and that would be particularly so for younger fitter Australians."
Elderly people and those with chronic illness need to be especially careful.
"The risk to these people goes up exponentially," Mr Johns says.
"These are the people we're most concerned for, they're over represented in particularly hot days like we've got today and like we've had over the last week."
Mr Johns says preparation is the key.
He's advising people to take simple measures such as wearing a hat, carrying water and staying out of the heat.
"The better you can prepare yourself, the better chance you have of getting through these extreme weather days with your health intact.
"Stay out of the heat, stay hydrated, stay cool, and stay in touch with those in your family and community that might suffer in today's high temperatures."
© ABC 2013
15:16 EST Two teenage girls have been taken to hospital after lightning strikes near their school oval in Sydney's south-west.