A bushfire is threatening lives and homes on the outskirts of Perth, prompting an emergency warning from firefighters.

The warning was issued for parts of Red Hill, Millendon, Herne Hill and Baskerville in the City of Swan on Tuesday afternoon.

The fire started near Toodyay Road in Gidgegannup and the alert was upgraded as it intensified.

The emergency warning applies to people bounded by Haddrill Road to the north, Campersic Road to the west, Neuman Road to the south and Red Hill Quarry to the east.

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Firefighters are actively combating the blaze and said residents should leave now for a safer place if the way was clear, or be prepared to shelter at home.

Aerial support has also been called in to assist crews on the ground.

A watch and act warning was also in place for people bounded by Burgess Road to the north, Toodyay Road to the south, Scott Road to the east and Red Hill Quarry to the west in parts of Gidgegannup.

Emergency services said the bushfire was moving in a north-westerly direction and was not contained or controlled.

Anyone unprepared should leave their homes now for a safer place, while those who planned to defend their homes should make final preparations.

People in the emergency warning area should leave in a westerly direction.