Tropical Cyclone Ilsa has strengthened to a Category 5 system before it hits WA's north-west coast either late Thursday evening or shortly after midnight, the Bureau of Meteorology confirmed at 3pm WST.

Ilsa is expected to cross between Port Hedland and Wallal Downs, with the area's between Broome and Whim Creek, around 700km of coastline, within the warning zone.

As of 2pm WST Thursday, the storm sits approximately 180km north of Port Hedland and 230 kilometres west northwest of Wallal Downs as it continues to bear down on the Pilbara and west Kimberely across the Indian Ocean.

As much as 300mm of rain is expected where Ilsa crosses the coast with extreme gusts of wind as high as 315km at its core between Pardoo Roadhouse and De Grey and 155km in surrounding areas.

Ilsa is forecast to weaken as it accelerates easterly over land between Parnngurr to Kiwirrkurra, and southwest of Balgo through Friday per latest updates from the BoM.

The last Category 5 cyclone to make landfall in WA was in 2007, when Tropical Cyclone George crossed the coast at a near identical point as projected for Thursday evening.

According to Nine News around $300 million of trade that moves in and out of Port Hedland each day has halted as the area prepares.

Additional emergency service personnel and resources have been sent into the area.

Evacuation centres have been opened at multiple locations.

Earlier on Thursday afternoon Department of Fire and Emergency Services (DFES) Commissioner Darren Klemm said time was critical for people in the area looking to evacuate.

At 3pm the BoM issued a Red Alert for people between Bidyadanga and Port Hedland (not including Bidyadanga) to Marble Bar (not including Marble Bar) to find shelter immediately.

"We do not want to see anyone outside of rated structures once the red alert is put on," Commissioner Klemm said.

Locals can call for Cyclone advice and DFES Alerts by dialling 13 3337 (13 DFES), check for latest updates on the BoM website and WA Emergency website and seek assistance from the SES on 132 500.

Call 000 in life threatening situations.