Penrith in Sydney's west has reached a top of 47.3 degrees Celsius, the highest temperature recorded by a weather station in the Sydney metropolitan area in 79 years.

The temperature hit 47.3C at Penrith just after 3:00pm on Sunday.

Sydney's hot pockets Suburb Forecast high Recorded high Penrith 45C 47.3C (3:25pm) Richmond 45C 46.3C (1:43pm) Campbelltown 42C 44.6C (2:27pm) Sydney - Observatory Hill 41C 43.4C (1:08pm)

The Bureau of Meteorology (BOM) early Sunday said it had confirmed preliminary data and declared it was the highest temperature ever recorded by a weather station in the Sydney metropolitan area.

However, the NSW BOM tweeted just after 4:00pm that they had missed a temperature in the north-western Sydney suburb of Richmond, at a now closed recording station.

The 1939 high was 47.8C.

A weak south-easterly change forecast to come through later on Sunday offering some relief to the coast.

Sydneysiders flocked to the beach to cope with the heat. ( AAP: Glenn Campbell )

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"That may just trickle into the western suburbs this evening, however the west is still expected to remain very hot for the rest of the day," said Andrew Haigh from BOM.

"Tomorrow will be another hot day in the west, a little bit less so than today in the east."

Total fire bans and severe fire danger warnings were issued by the NSW Rural Fire Service for the Hunter and Greater Sydney, with the bans continuing into the start of the working week.

Sydney's heatwave caused problems at the Sydney International tennis, with fifth seed Kristina Mladenovic retiring after being badly affected by the heat.

Extreme, severe and low-intensity heatwave ratings have been given to most of NSW over the next few days. ( Supplied: Bureau of Meteorology )

The competition was out at Sydney Olympic Park, which had a top recorded temperature of 44.5C just after 1:00pm.

Bahar and Amir Kashefi were beaming bright on their wedding day despite the heat. ( ABC News: David Spicer )

Bahar and Amir Kashefi were still smiling despite the heat scorching their wedding day.

"I'm sweating, my bridesmaid is sweating. The wind was not too bad around here but otherwise it was scorching hot," the bride said.

"I think I am going to cut the wedding short, go straight back to the hotel and jump in the pool."

Homeless man Charles Orchard, 43, receives water from Missionbeat van driver Patrick Crawford near Central Station. ( ABC News: Emily Laurence )

Mission Australia's homeless transport service Missionbeat were out in force to keep people cool.

They organised for two heat-affected homeless people to get to the hospital and transferred several others to refuges and hostels.

Animals at Taronga Zoo on Sydney's north shore were fed a variety of iced foods to keep them cool, with Fergus the Hippo feasting on some carrot ice blocks.