A tropical cyclone off northern Western Australia is expected to intensify into a severe category three system.

Cyclone Mitchell was offshore of Port Hedland and moving south-west towards the coast off Karratha late Saturday morning.

Authorities expect the cyclone to continue churning south-west and cross the western Pilbara coast late Sunday afternoon.

It was expected to intensify into a category three system as it passes just north of Karratha Saturday night and track close to the Pilbara coast on Sunday.

Very destructive wind gusts could reach 170km/h on Saturday night around Karratha, Dampier and Wickham, and Onslow further south during Sunday, according to the Bureau of Meteorology.

A watch and act warning was in place for Whim Creek to Mardie including Barrow Island and Montebello Islands, with residents told to prepare to take shelter due to the potential threat to lives and homes.

Residents from Pardoo Roadhouse to the east of Whim Creek, and from south of Mardie to Carnarvon and Pannawonica, were advised to monitor conditions and prepare for dangerous weather.

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An evacuation centre was being opened at Karratha Leisureplex from midday Saturday, with people advised to bring essential items such as medication and identification with them but not pets.

The ports of Ashburton, Cape Preston West, Dampier, Port Hedland and Varanus Island have all be closed as the weather system approaches.

Up to 130mm of rain was predicted for Port Hedland on Saturday, bringing with it the risk of flash floods.

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

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

The cyclone’s impending arrival comes as other outback towns are still feeling the brunt of major flooding.

In the Northern Territory, more than 400 people who bussed 230km to Darwin from Daly River on Wednesday may have to wait days before they can return, as riverine flooding is not expected to peak until early next week.

Incident controller Supt David Moore said 298 evacuees, including 110 children, were housed at the Foskey Pavilion at the Darwin Showgrounds.