With a flood warning in place for the midwest Gascoyne region on Sunday, roads remain closed and residents are urged to watch for fast-flowing and rising waters.

Premier Mark McGowan said the tropical low-pressure system sweeping across the state had caused considerable damage, including to the Northwest Coastal Highway.

He said some closures were likely to remain in place for several weeks but authorities were already working to open the highway as soon as possible.

"Road building crews are ready to deploy as soon as flood levels recede sufficiently to make an on-the-ground assessment of the damage," he said.

Heavy rains and strong winds were also expected to hit Perth and parts of the state's southwest on Sunday and into Monday as the low moved down the coast.

A severe weather warning was in place for the southwest, lower southwest and Great Southern districts.

Locations that may be affected include Bunbury, Busselton, Collie, Manjimup, Margaret River, Augusta, Dunsborough, Harvey and Walpole.

The Bureau of Meteorology said rainfall of up to 100 millimetres is possible in some areas with winds gusts likely to hit 100 km/h.

Tides are also likely to be higher than predicted along the west coast north of Augusta with the potential for flooding in low-lying coastal areas.

The heaviest rainfall recorded to 8am on Sunday included 85mm at Lancelin East and 80mm at Hill River Springs.

The highest wind gusts were 100km/h at Gooseberry Hill and 94km/h at Bickley.

Since 9am on Friday, emergency services have responded to more than 110 calls for assistance.

Mr McGowan said the severe weather came after a challenging week with parts of the state also enduring a five-day lockdown because of a coronavirus outbreak, and bushfires in the Perth Hills.

Australian Associated Press