'Harrowing' night as cyclone devastates remote towns

Residents in the firing line of a destructive cyclone are grappling with the "devastating" aftermath of an overnight battering.

Ex-Tropical Cyclone Narelle was downgraded to a tropical low on Saturday, but not before it lashed parts of Western Australia's coastline.

The storm left a trail of destruction in parts of the Pilbara and North West Cape, including Exmouth, a holiday town 1250km north of Perth.

"There's pretty much devastation everywhere you look," Exmouth resident Craig Kitson told AAP.

"The town has fundamentally changed."

The town's few thousand residents bore the brunt of the category four storm, as it brought winds in excess of 250km/h on Friday.

Roofs were torn off buildings, power was lost, homes were flooded and about 50 people had to abandon a local evacuation centre when it sustained wind damage.

Though he lost a fence and spent the night under a leaking roof, Mr Kitson counts himself lucky.

"It was definitely a harrowing night there for a lot of people" Mr Kitson said, adding some homes had been completely destroyed.

"Some people's lives have been drastically changed."

While authorities are still counting the losses, locals say the storm felt as bad as any in recent memory, Mr Kitson said.

"There was a category five in 1999 that probably did more damage but that's just because the building code has changed," he said.

"People reckon this one was worse because it was longer and we definitely caught the bad side of it."

Thousands of homes and businesses remained without power across Exmouth and Carnarvon on Saturday morning.

Nearly 40 Pilbara residents had requested assistance from the SES by Saturday morning, including 29 in Exmouth, a spokesperson said.

Narelle tracked south to Coral Bay and made landfall on Friday evening just south of the tiny town before weakening to a category three system.

It was downgraded to a category two northeast of Kalbarri and Geraldton before becoming a tropical low on Saturday morning.

Overnight, gusts above 120km/h were recorded in parts of the Gascoyne, alongside rainfall totals of up to 100mm, increasing the risk of flash flooding and road closures.

It will continue to lose intensity as it moves inland but is still producing powerful wind gusts and heavy rainfall, the bureau said.

A watch and act alert remains in place west of Onslow to Coral Bay, with advice level warnings covering much of the state.

A flood watch is in place from Exmouth as far south as Perth's Swan River, with the system expected to pass east of the state's capital on Saturday afternoon.

It is expected to continue moving southeast until crossing into the Southern Ocean on Saturday evening.