Mitchell strengthens as it nears the WA coast.

Tropical Cyclone Mitchell has strengthened to a category three storm as it nears the Western Australia coast, bringing with it damaging wind gusts of up to 185 km/h.

Residents from Whim Creek to Onslow, including the mining town of Karratha, have been told it is too late to leave and they must seek shelter indoors immediately, with Mitchell presenting a threat to lives and homes.

The storm was north of Dampier and tracking southwest closer to the west Pilbara coast in the early hours of Sunday, where locals are being warned to expect heavy rain and severe flash flooding.

Mitchell is expected to make landfall between Onslow and Exmouth on Sunday night before taking a more southerly track over land on Monday, Emergency WA warned.

The wind gusts in some areas may reach up to 205 km/h on Sunday morning if Mitchell moves closer than forecast, the Bureau of Meteorology warned.

"Damaging to destructive winds are expected to ramp up in the next 24 hours," bureau forecaster Angus Hines said on Saturday.

"Those winds are strong enough to bring down big branches or entire trees, damage property, and lead to power outages."

An evacuation centre has been set up at Karratha Leisureplex, and a second evacuation centre is being opened further south at the Onslow Multi Purpose Centre.

Authorities warn the central and west Pilbara coast faces the risk of flash flooding throughout the weekend, with the west Gascoyne region likely also affected by Monday.

Abnormally high tides will also present a serious flood risk for the Karratha region in the early hours of Sunday and towards Onslow Sunday afternoon, the bureau says.