Temperature records have been broken as a heatwave continues across the country and parts of South Australia are expected to enter catastrophic fire conditions later on Friday.

Marble Bar in north-western Western Australia broke its all-time heat record on Thursday, reaching 49.3C.

In northern Victoria, Mildura had another day of temperatures in the mid-40s, reaching 44C on Thursday. In New South Wales, Menindee, near Broken Hill, and Wentworth, near the Victorian border, peaked at 45C.

Marble Bar hit a max temperature of 49.3°C today; its hottest day since temperature records began there in 1901. The airmass over inland WA is one of the hottest we've ever seen, and is causing a severe to extreme #heatwave over large parts of the country. pic.twitter.com/1Da3Hse19v — Bureau of Meteorology, Western Australia (@BOM_WA) December 27, 2018

Summer in Australia...melting roads, truly ‘Piping Hot’ thongs, tarred foot, and a 10 km-plus traffic jam heading towards Bateman’s Bay. @smh pic.twitter.com/T8LGuUJBKu — Peter Hannam (@p_hannam) December 27, 2018

On Friday, the Bureau of Meteorology was forecasting 41C for Penrith, 37C for Parramatta and 30C for the Sydney CBD itself. The Sydney region was not forecast to have a day below 30C until at least mid-next week.

The highest warnings were in place for South Australia, which was expecting temperatures of 48C at Oak Valley, north of the Nullabor, and 47C at Port Augusta.

“The previous December record is also 47C from three years ago so we might see some records tumble there today,” said Diana Eadie, a meteorologist at the bureau.

The bureau forecast that catastrophic fire conditions could set in later on Friday in parts of South Australia when strong southerly winds were expected to hit the state.

The mid-north fire ban district of South Australia, which takes in towns including Clare, Snowtown, Burra and Jamestown, was on alert for catastrophic fire conditions.

By Friday morning, temperatures in Snowtown had already reached 38C.

Five other fire ban districts in the state – the west coast, the eastern Eyre Peninsula, Flinders, the Yorke Peninsula and the Mount Lofty Ranges – had extreme fire danger ratings and there were severe fire danger ratings in place in three others.

The South Australian Country Fire Service was warning residents in these areas to be ready to enact their bushfire survival plans.

“It’s won’t be a viable option in some parts of the state to stay and defend today because conditions will be so bad,” said Alison Martin, a spokeswoman for the fire service. “We’re telling people to enact their bushfire survival plan early and, if they need to leave, they need to do so before they see smoke and know where they’re travelling to.”

In Victoria, the Mallee and Wimmera regions had severe fire danger ratings on Friday.

Further south, Melbourne was expecting a top of 34C on Friday before some slightly cooler weather over the weekend. But the relief would be short-lived, with temperatures forecast to climb again next week.

“We’re seeing a resurgence of well above average temperatures in the mid to late part of next week for south-east Australia,” Eadie said. “The areas being impacted now in NSW and into parts of Queensland, there’s no real cool change coming through at this stage.”

Temperatures in much of the country were sitting at 5C to 15C above average for this time of year, with only a few places escaping the heat.

“The tropics aren’t so bad at the moment with the rain,” Eadie said. “And parts of Perth haven’t been particularly hard hit.”