In Albion Park the temperature peaked at 45.8 degrees at 1.16pm, the highest ever recorded there.

The previous record at the Bureau of Meteorology weather station at Albion Park was 45 degrees recorded on New Year's Day 2006.

Yesterday, it got to 45 degrees in Kiama (1.45pm), 42.4 in Bellambi (12.48pm) and 45.4 at Nowra (3.11pm).

Most of the region was sweltering under oppressive, 40-degree heat by 11am. In Albion Park it was still more than 42 degrees at 5.30pm.

The conditions caused water from taps marked cold to run as warm as a bath. The air was very dry - about 15 per cent humidity in Albion Park.

In Wollongong, Crown St cafe Lee and Me closed early, at 1pm.

"People want to be at the beach or somewhere cool on a day like this," said owner Naomi Hudson.

Wollongong lifeguards extended their hours until 7pm on all beaches to accommodate hordes of late swimmers.

The temperatures were about five degrees higher than forecast.

There were multiple triple-0 calls for cases of heat exposure, including for a 70-year-old man at Windang, a 45-year-old woman at Austinmer Beach and a 26-year-old man at Cordeaux Heights, who was working on machinery when he succumbed to the effects of heat exhaustion.

Statewide, the Ambulance Service of NSW had responded to 44 cases of heat exposure - one third of whom were for people over 60 - by 3pm.

Over the same period there were 89 reports of people falling unconscious or fainting and 37 instances of vomiting.

"Many of those cases are attributable to the heat," an ambulance spokeswoman said.

It was also the hottest day in recorded history in Sydney, which experienced more heat-related illness, transport chaos and even melting roads and ice rinks.

The mercury hit 45.8 at Sydney's Observatory Hill at 2.55pm, exceeding the previous record of 45.3 set on January 14, 1939.

The record temperature was similar to that recorded in places in the NSW far west, such as White Cliffs, which sweated the day out in around 44-degree heat.

That was topped by temperatures in Penrith, in western Sydney, which reached 46.5 degrees.

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 John Ambulance spokesman said the organisation treated 200 people, mostly for dehydration.

At the Australia Youth Olympics, basketball, golf, canoe and athletics events had to be cancelled or postponed because of the soaring temperatures.

Most trains across the CityRail network were delayed by at least an hour yesterday when overhead wiring and signal problems failed to cope with the extreme heat.

In Wollongong the bureau forecasts a far milder day today (maximum 22, chance of a storm) and tomorrow (maximum 23, shower or two).