An emergency warning has been issued for parts of Melaleuca and Jandabup in Wanneroo, about 36km 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 is moving fast in a westerly direction and is not contained or controlled.
"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, but nearby residents have been warned to remain alert.
A watch-and-act caution remains in place for parts of Hammond Park, about 30km south of the city.
An emergency warning was in place 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 Rd.
The fire initially closed the freeway but it has since reopened.
🌡� Temperatures across the — Bureau of Meteorology, Western Australia (@BOM_WA) #Perth metro area remain 12-14°C above average for the rest of this week.🥵 Severe #Heatwave conditions continuing.⚠� See the warning https://t.co/T7yEk1nyj5@WAHealth @dfes_wa pic.twitter.com/Xzp2UHa3tTNovember 22, 2023
Western Australia is experiencing a spike in temperatures, with the mercury topping 37C on Wednesday and forecast to hit 40C on Thursday.
No relief from the heat is expected before Monday.
3°C