Passengers were stranded in a broken down train without air conditioning near the Sydney Harbour Bridge as temperatures soared to 39 degrees soon after Australia's most famous horse race was won.

At Mascot, in Sydney's south, the temperature reached 39.2 degrees at 3.43pm (AEDT) on Tuesday, with similar top temperatures of 38.8 degrees recorded at Campbelltown, in Sydney's west, and 36.2 degrees at Terrey Hills, in Sydney's north.

North of Newcastle and in the Hunter Valley, fire crews battled blazes that threatened homes and forced residents to evacuate.

For a November day it was nothing unusual, Peter Zmijewski from the Bureau of Meteorology told AAP.

"These kinds of temperatures do happen in November," he said.

"They don't happen every week, but every spring we see a couple of days that go to very high temperatures, then it cools down, because there are a lot of adjustments in the atmosphere."

The temperature reached 36 degrees in Sydney's CBD when a power failure caused a train to stall just short of the platform at Milsons Point Station, in Sydney's north, about 4.05pm (AEDT).

Commuters were freed about 40 minutes later.

CityRail chief operating officer Andy Byford said the time it took to get the passengers off the stranded train was reasonable.

"It appears it (the train) was half off the station, half on the station," he told Macquarie Radio.

"The difficulty that presented us with was that if we were to ... get the passengers off, we could have done that through the driver's compartment.

"We did look at it, but had we done that, then it would have taken a long time marching everyone through the train safely in between carriages to get them off.

"We took the decision that it would be better to get the train moving, not least because there were other trains behind that train caught between the stations."

Opposition Leader Barry O'Farrell said contingency plans should have been in place.

"Surely there are back up procedures that guarantee to customers not only that their safety will be looked after but when it's as hot as it is today they'll be out of those trains and into the shade as soon as possible," he told Macquarie Radio.

Racegoers at Royal Randwick racecourse and Rosehill did their best to stay hydrated in the scorching heat as Shocking won this year's Melbourne Cup.

Staff at Royal Prince Alfred and Liverpool hospitals did not need to treat any patients for heat exhaustion, a spokeswoman told AAP.

No properties were damaged when bushfires broke out north of Newcastle and in the Hunter Valley.

Several elderly people were evacuated from their homes in Rosemount Drive, Raymond Terrace when a fire jumped the nearby Pacific Highway on Tuesday afternoon.

Firefighters had the upper hand on the fire by 8pm (AEDT) on Tuesday, but did not expect to contain the blaze for several hours.

A separate fire also threatened 10 homes on Rosemount Road and Reg Thornton Memorial Drive, Denman, in the Hunter Valley.

The fire was contained early on Tuesday evening.

Cooler conditions are expected on Wednesday, with a top temperature of 22 degrees forecast for the Sydney CBD.