Temperature records have already been broken but the worst of the heatwave sweeping across parts of Australia is yet to come.

The Bureau of Meteorology warned Friday will mark the peak of the week-long heatwave — currently in its fifth day — for some of NSW’s most heavily populated areas. Temperatures in western Sydney are expected to slide well into the 40s, while the CBD is likely to have its fifth consecutive day above 30C for the first time in eight years.

Fri marks peak day for some of #NSW most heavily populated areas.Temps in western #Sydney well into the 40's, regional western towns similar after many broke records this week, CBD likely to have 5th consecutive day above 30 for 1st time in 8 yrs https://t.co/RASIcXxP9R #heatwave pic.twitter.com/TH5RfrrPNl — Bureau of Meteorology, New South Wales (@BOM_NSW) January 17, 2019

On Thursday, a total of 27 places across NSW and the ACT baked in record maximum temperatures, with one town in the northwest of NSW sweltering in oppressive, all-time high heat for two straight days.

The freakish temperatures have turned forecast maps a worrying black and purple in areas where the mercury is set to spike.

Whitecliff, a tiny outback town with a population of just under 150 people, broke its record on Wednesday with a temperature of 48.2C, dropping only marginally on Thursday with a high of 47C just after 3pm. The extreme heatwave emptied the streets, turning it into a scorching ghost town.

Elsewhere in the far northwest, Tibooburra Airport recorded the top temperature in the state on Thursday with 48.2C just before 4.30pm.

"Severe to extreme heatwave conditions across the southeast interior". Temperatures exceeding 45oC for many locations through western NSW and central Australia this afternoon. Latest at https://t.co/QwFMlibmFD pic.twitter.com/LLmQj2eAJ1 — Bureau of Meteorology, Australia (@BOM_au) January 17, 2019

Noona recorded 48.1C and Wilcannia Airport and Smithville both reached 47.8C, with Borrona Downs, Bourke, Cobar Airport and Delta all reaching temperatures of at least 47C.

In Sydney’s west, Penrith, Richmond, Campbelltown and Camden all reached 35C by 1pm.

Conditions are so extreme that the bitumen on the Oxley Highway near Wauchope, just west of Port Macquarie, began melting about midday.

Looking ahead, the Bureau of Meteorology has warned of more sweltering weather on the way for much of the state.

In a statement, BOM spokeswoman Anita Pyne said the west of NSW would likely see temperatures in the mid to high 40s, including areas around the Ivanhoe and Menindie areas forecast to hit up to 48C.

Broken Hill is forecast to reach four consecutive days of more than 45C — an event which has not happened since records began in 1957.

When will the #coolchange arrive? The hot weather is easing through southern & western #SouthAustralia today, will ease in #Victoria on Friday, & southern & central #NSW on Saturday. Unfortunately the heat will linger over northeast SA & NSW. Latest info: https://t.co/9H4auv9MbK pic.twitter.com/8oO5GobDms — Bureau of Meteorology, Australia (@BOM_au) January 17, 2019

Transport for NSW is warning drivers to allow extra time on the roads as dangerous temperatures often result in more breakdowns as vehicles overheat.

Meanwhile, the NSW Rural Fire Service is battling more than 60 fires across the state, and 13 fire bans are in place across much of central NSW, stretching from the Victorian border up to Queensland.

Authorities are again warning people to take extra care in the heat by staying indoors, keeping hydrated and limiting physical activity.

Paramedics have been called to treat numerous patients for heat-related illnesses, including three children in Sydney’s southwest who were suffering from exhaustion, heatstroke and vomiting. One was taken to Liverpool Hospital in a stable condition.

Sydney train users are being warned there could be delays across the network as temperatures rise.

Temperatures in Sydney’s west are expected to climb as high as 45C on Friday, ahead of a long-awaited cool change on Saturday.