Residents in Perth have been warned it is too late to leave their homes after a fast-moving out-of-control bushfire threatening two northern suburbs forced earlier evacuations.

An emergency warning was issued for parts of Melaleuca and Jandabup in Wanneroo, about 36 kilometres north of the city centre.

“It’s too late to leave for people east of Hawkins Road,” the Department of Fire and Emergency Services said on Wednesday.

“You are in danger and need to act immediately to survive.”

The fire started near the intersection of Boundary and Bustard roads in Mariginiup.

It was moving fast in a westerly direction and was not contained or controlled.

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“You need to shelter in your home in a room away from the fire front and make sure you can easily escape,” emergency services said.

“You must shelter before the fire arrives, as the extreme heat will kill you well before the flames reach you.”

Meanwhile, a bushfire in Perth’s south has been downgraded, although residents have been warned to remain alert.

A watch-and-act caution remained in place for parts of Hammond Park, about 30 kilometres south of the city.

There was an emergency warning earlier on Wednesday for the suburb, along with Aubin Grove and Wattleup.

The blaze started near the intersection of the busy Kwinana Freeway and Rowley Road.

The fire initially closed the freeway but it has since reopened.

Western Australia is experiencing a spike in temperatures. The mercury topped 37 degrees on Wednesday and is forecast to hit 40 degrees on Thursday.

No relief from the heat is expected before Monday.

-AAP