Perth has recorded its fourth consecutive day of temperatures above 40 degrees Celsius, equalling a record that has stood for more than 80 years, as a heatwave continues to grip the city.

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The temperature peaked at 40.3C in Perth at 11:30am on Wednesday.

The last time the city recorded four consecutive days above 40C was in 1933.

However, the Bureau of Meteorology (BoM) said it was unlikely the record would be broken on Thursday, with a slightly lower 38C forecast for the metropolitan area.

"That's only happened once before since we started records in 1897, and that was back in 1933 when we had a run of four [days of] forty degrees or more from the 7th to 10th of February," BoM forecaster Neil Bennett said.

"If we do get another day, which at the moment looks highly unlikely, then that would be a new record, but we don't think that that's going to happen.

"We think temperatures will be below 40C tomorrow. [It's] still going to be very hot though, we're looking at temperatures of around 38 degrees."

Mr Bennett said Perth had also now recorded its most number of 40C days in any one summer.

A bitumen road melts after the temperature reaches the low to mid 40 in Mingenew in the Mid West. ( ABC News: Joanna Prendergast )

"Yesterday we equalled that record of six, but now we have set a new record. We've had seven days of 40 degrees or more in summer," he said.

"We've had two in December, one in January and now four in February."

"We had a very mild start [to February] - we had one of the coolest nights on record for February - so it did start off very mild, but it warmed up very quickly towards the back end of last week."

The hottest place in the metropolitan area on Wednesday was Pearce, north of Perth, where the temperature reached 45.1C.

Meanwhile Gooseberry Hill in the city's east recorded 44.2C.

But Roebourne Airport in the Pilbara posted WA's hottest temperature at a sizzling 46.4C, while nearby Karratha recorded 45.3C.

The temperature in Perth is expected to drop to 35C on Friday and 33C on Saturday and Sunday.