Severe easterly winds have hampered efforts to fight an unpredictable bushfire threatening lives and homes in Perth's north-eastern suburbs, and there are concerns conditions could get even worse.

Key points: The bushfire started in the Walyunga National Park on Monday

The bushfire started in the Walyunga National Park on Monday Strong winds of up to 90kph are forecast today, hampering firefighting efforts

Strong winds of up to 90kph are forecast today, hampering firefighting efforts Residents are being urged to stay vigilant and be alert for changing conditions

About 170 firefighters spent the night battling the blaze near Bullsbrook, with authorities saying it is currently stationary on the east side of the Avon River in the Walyunga National Park.

But there are fears the fire or embers could jump the river and burn quickly towards properties in the Shady Hills Estate, where about 130 of the firefighters are in place.

An emergency fire warning remains 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.

A separate bushfire watch and act warning is in place, along with a low-level advice. ( Supplied: Emergency WA )

Residents have been warned to act immediately to survive, and have been urged to leave their properties and seek alternative accommodation.

The Bureau of Meteorology (BOM) said severe easterly winds created challenging conditions overnight and there were concerns gusts could intensify.

"Last night we saw a really strong east-south-easterly surge move over the Hills and then through the Perth metro area," BOM duty forecaster Pete Clegg said.

"This morning there is the chance that we see those winds strengthen, there's some really strong winds aloft above the surface and they could mix down.

"So there certainly [is] still the risk that we see some wind gusts pushing upwards of 90 kilometres per hour this morning, and that does include around some pretty sensitive fire sites around the Bullsbrook area."

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'The situation remains serious': DFES

Department of Fire and Emergency Services (DFES) incident controller Peter Sutton said the situation remained delicate, given the wind conditions and difficult terrain.

"The conditions overnight were as forecast … due to the terrain we didn't have much luck in trying to track the whole fire, so we can't give a contained or controlled message just yet," he said.

"We also had about 25 structural vehicles up in position in the Shady Hills Estate to protect properties in case that fire did take a run up the hill towards the estate from the Avon River.

"So really an amazing effort from firefighters from all services overnight in very trying conditions, but at this stage the situation still remains serious."

Shady Hills Estate can be seen just across the valley from the fire field. ( ABC News: James Carmody )

Superintendent Sutton said authorities were doorknocking overnight telling residents to leave, but a number of them had chosen to stay and defend their properties, and he urged them to stay vigilant.

"[The threat] will start easing off but only slightly after midday, where we're still having easterlies gusting up to 50kph, and that's when the temperature starts to increase," he said.

"We're looking at about 31 degrees Celsius so that's when we have real concern. So by no means has the risk passed."

Water bombers including three fixed-wing aircraft and two helicopters are helping to fight the bushfire.

Residents say fire zone looked like a 'fairyland'

Resident Steve Thomas said spending a night away from his property was unnerving.

Steve Thomas left his property behind in the fire zone. ( ABC News: Frances Bell )

"We left our property, had a few things packed and the dogs ready to go, and went down the end of the street just to see what was happening," he said.

"And from what I saw at night, all the embers were very well lit up, it was like fairyland.

"So from that assessment I thought 'one wind change and it will be too late', because there's steep hills with a lot of grass on them, and in three minutes it would be up to our place.

"The first time you spend a night out of your own house, it's quite unnerving."

An emergency warning is in place for the fire, which has burnt through more than 83 hectares. ( ABC News )

Evacuation centre set up

A watch and act alert is in place for people west of the Shady Hills Estate, west of the Avon River, north of Walyunga 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.

A temporary evacuation centre has been set up at Altone Park on Benara Road in Beechboro, but people are being urged to only take essential items with them.

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

A community meeting will be held at 5:00pm at the Ethel Warren Bullsbrook Community Centre on Maroubra Avenue.

Water bombers have resumed tackling the fire near Bullsbrook this morning. ( ABC News: James Carmody )

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.

It is unclear what caused the blaze, which has forced the closure of the national park.

Intense winds, high temperatures and no rain

Mr Clegg said the hilly landscape of the Darling Scarp could exacerbate the strong winds.

"There's definitely the chance that we get acceleration with some down-slope acceleration going on, but it can be quite a tricky situation to diagnose exactly where those stronger winds will occur," he said.

"Particularly in terrain around the valleys and that sort of thing, whilst it could be a little bit more sheltered from an east-south-easterly wind, there is also the potential for that downslope acceleration and even funnelling to occur through the valleys."

Mr Clegg said the intense dry easterlies came on the back of a very hot start to the week and there was no rain expected to help the situation.

"There's no risk of thunderstorms, which is great news in terms of there's no additional source of extra fire sites being ignited in that regard," he said.

"But [there's] no precipitation really to help conditions out in terms of fighting fire, so it's a bit of a double edge with that one."