An emergency fire warning has been issued for parts of Bullsbrook in Perth's north-eastern suburbs where crews are battling an unpredictable blaze.

The warning has been issued for people the vicinity of Shady Hills Estate south of Smith Road in Bullsbrook, and in the vicinity of Ewing and O'Brien roads in Gidgegannup, and the Walyunga National Park in the City of Swan.

Homes are under immediate threat in Shady Hills Estate.

People in the emergency warning area are being urged to act immediately to survive.

Residents were urged to seek alternative accommodation for the night, due to what authorities describe as "expected, unpredictable, severe fire weather".

An emergency bushfire warning has been declared for an area near Bullsbrook. ( Supplied: Emergency WA )

Changing conditions and inaccessible terrain made it difficult for firefighters to battle the blaze overnight.

Winds in the area were expected to reach 80 kilometres per hour, which can cause embers to travel well ahead of the fire front.

The blaze is currently stationary, but authorities say the strong easterly winds are likely to cause extreme fire behaviour in the early hours of the morning.

Department of Fire and Emergency Services (DFES) incident controller Peter Sutton said about 170 firefighters from a range of services were fighting the blaze.

The fire is being fought from the air and the ground. ( ABC News: Emily Piesse )

"Basically they're fighting a fire in very steep terrain. The fire run is uphill towards Walyunga National Park, but that area of the fire is probably not our greatest concern," he said.

"That area of the Shady Hills Estate, which is mentioned in the emergency warning, is our biggest threat.

"If this fire does jump the [Avon] river, it will travel up that hill very quickly up to those properties in the Shady Hills Estate.

"Firefighters will not have any air support available to them and it will be near impossible to stop … the fire behaviour will move so quickly beyond those properties.

"We're putting in strategies with retardant, where we drop them from aircraft at the back of those properties to try to reduce the rate of spread if that fire does take off during the night.

"If you're not prepared to stay and defend your property, please leave early."

A temporary evacuation centre has been set up at Altone Park on Benara Road in Beechboro.

People are being urged to only take essential items the evacuation centre — alcohol and pets, with the exception of guide dogs, are prohibited.

Firefighters are expected to have difficulty fighting the blaze overnight. ( ABC News: Emily Piesse )

Horses can be taken to the State Equestrian Centre pony club.

Bushfire watch and act

A watch and act alert is in place for people west of the Shady Hills Estate, west of the Avon River, north of Walynga Road and east of Great Northern Highway in Bullsbrook, and north-western parts of Walyunga National Park.

There is a possible threat to lives and homes in those areas as the fire approaches and conditions change.

Vehicle control points have been set up at the intersections of Taylor and Clarkson roads, Ewing and Clenton roads, and Taylor Road and Foaling Ridge.

The fire started near the intersection of Taylor Road and Jilcrai Road in the Walyunga National Park, and has so far burnt through more than 83 hectares.

The national park has been closed.

It is unclear what caused the blaze.