Maximum temperatures are forecast to exceed 40C in some parts of the Pilbara in Western Australia, down to the SA coastline and into inland NSW over the coming days.

Already the mercury has climbed to 39C in Port Hedland in WA and will stay in the high-30s and low-40s for the best part of the next week.

The NSW town of Bourke, not far from Queensland border, is predicted to hit a record-breaking four-day streak of 40C days from Thursday to Sunday.

The temperature is due to drop to just 39C on Monday.

Four consecutive days of 40C temperatures have not been reported so far into autumn in more than 150 years of records.

A streak of temperatures above 35C will also hit Dubbo, in the NSW central west, from Thursday to Sunday.

This is at least 6C above the average March temperature of 29C.

The “unseasonably hot” temperatures will arrive on the east coast just a few days out from the autumn equinox.

“The prolonged nature of the coming hot spell is quite remarkable,” Weatherzone meteorologist Anthony Sharwood said.

Extreme heat will be focused on NSW’s far west, though western Sydney temperatures could soar to 40C while the city experiences heat in the mid-to-high 30s.

Sydney will cop the brunt of the heat on Thursday, with tops of 34C expected in the centre of the city.