A child has been taken to hospital with heatstroke during a day of extreme temperatures across NSW.
At 12.45pm on Wednesday ambulance officers attended Cabramatta West Public School, in Sydney's southwest, where three children were experiencing vomiting, exhaustion and heatstroke, a spokesman said.
One was taken to Liverpool Hospital in a stable condition.
"They had hats on, they tried to stay in the shade, but unfortunately it wasn't enough today, so best to stay inside," NSW Ambulance's Tatalia Noor told 7 News.
By midday on Wednesday the mercury had soared beyond 45C throughout the state's central west and at 3pm Wilcannia, Mulurulu, Ivanhoe and Hay topped 47C.
Whitecliff in the northwest, recorded the highest temperature in NSW and an all-time high for the area with 48.2C just before 3.30pm.
Nine areas in total broke temperature records around the state.
The majority of NSW is expected to exceed 41C from Wednesday to Friday, something the Bureau of Meteorology says hasn't been seen in 80 years.
Record heat in South Australia on Tuesday moved into much of western and central NSW on Wednesday, a Bureau spokesman told AAP.
BoM weather services manager Jane Golding said much of the state will peak on Friday before a cool change on Saturday. Penrith is forecast to reach 45C with coastal Sydney to hit 34C while 47C is expected to continue in western NSW.
Very hot, dry and windy conditions were predicted to generate elevated fire dangers for the remainder of Wednesday and into Thursday.
Fire warnings were issued for the south and central ranges, the lower central west plains, the southern slopes, north western and eastern Riverina fire areas just before 5pm.
Total fire bans are now in place for the central ranges, north western and southern slopes areas.
Sydney rail commuters are being warned there could be delays across the network as temperatures rise.
Air conditioned trains scheduled for routine checks will be returned to service, while extra maintenance and medical staff are on stand-by.
"There's very little we can do when you've got this degree of heat hitting steel tracks (but) at the same time we want to make sure we've got the staff on board as quickly as possible to be able to respond," NSW Transport Minister Andrew Constance told reporters.
Energy Minister Don Harwin said measures in place would meet energy demands during the next few days and residents shouldn't be worried about using air conditioners.
Authorities are reminding people to stay indoors, minimise physical activity and keep hydrated, especially people over 75 and those with chronic medical conditions.
City air quality is also expected to worsen because of the heat, with high ozone levels forecast.
Australian Associated Press