A severe tropical cyclone brewing north of Western Australia has intensified more rapidly than expected, reaching a category four severity and prompting warnings of heavy rainfall, damaging winds and a destructive storm surge along coastal areas.

Key points: Veronica is predicted to develop into a category five cyclone on Friday

Veronica is predicted to develop into a category five cyclone on Friday It is not clear exactly where it will cross the Pilbara coast

It is not clear exactly where it will cross the Pilbara coast Widespread heavy rainfall, storm surges and major flooding are forecast

Cyclone Veronica is sitting about 355 kilometres north-west of Port Hedland but is expected to approach the Pilbara coast with "potentially drastic impact" over the weekend.

The slow-moving system is tracking south-west, but is expected to veer towards the coast after developing into a category five system on Friday.

"Veronica is over some very warm waters well north of the Pilbara coast with low vertical wind shear which has made it possible for Veronica to rapidly intensify over the last 24 hours," Bureau of Meteorology (BOM) senior forecaster Matt Boterhoven said.

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He said it was still not quite clear exactly where and when Veronica might cross the coast, but communities from Pardoo to Mardie, including Karratha and Port Hedland, remained on blue alert.

"So people in between Mardie and Pardoo should be prepared for cyclonic weather and listen to emergency messages coming out from DFES (Department of Fire and Emergency Services)," he said.

"We'll see gales develop maybe as early as Friday evening, but more likely during Saturday and they'll [possibly] extend east to Wallal Downs and further west to Onslow.

"We'll see destructive gusts develop … possibly late Saturday and very destructive winds in excess of 165 kilometres per hour are possible."

Mr Boterhoven said conditions for Cyclone Veronica would be less favourable as it approached the coast, so it could weaken to a category four.

"That's still going to have a potentially drastic impact for the Pilbara region, so people have got to be well aware of major flooding around the Pilbara coast and [they] could see some very dangerous storm tides," he said.

The centre of the system has seen sustained winds of 165 kph, but gusts of up to 230 kilometres per hour have also been recorded.

Wind map showing Tropical Cyclone Veronica off WA's north

The BOM has warned widespread heavy rainfall conducive to major flooding is likely along the Pilbara coast over the weekend and into early next week.

Communities warned to start preparing

The blue alert area includes the communities of Mardie, Pardoo, Port Hedland, South Hedland, Wickham, Roeburne, Point Samson, Karratha and Dampier.

Although there is no immediate danger, those communities have been asked to start preparing, to secure or remove loose materials from around their homes and to ensure they have an emergency kit ready to go.

Karratha Mayor Peter Long said the city was following standard procedures in cleaning up all outdoor areas so that the town was ready.

"We need to take it seriously. If it hits, it's very dangerous," Mr Long said.

"There will be very high winds with things flying around."

Mr Long said residents should start take the necessary precautions and urged people to go to a refuge if required, warning parts of the town could go under water due to storm surges.

"DFES will advise when you need to do this, but we have the Leisureplex which has been designed as a structure for this purpose," he said.

'This is a serious event': DFES

With extra emergency services staff and volunteers heading to the Pilbara to be on hand for the clean up, DFES Acting Chief Superintendent Paul Carr urged residents to prepare their homes now.

"There hasn't been a cyclone up in that part of the world for some time, so we are concerned about some level of complacency slipping in," he said.

Veronica is expected to develop into a category five cyclone on Friday. ( ABC News: James Carmody )

"This is a serious event and we are taking it as that.

"If you don't need to be there and you feel uncomfortable, it is time to leave early."

Superintendent Carr said residents needed to keep up to date with the latest warnings, ensure they have a battery operated radio in case there was a power outage, secure loose items around their home and stockpile supplies.

"In getting your emergency stocks ready, start thinking about what food stocks you'll need and water you'll need, bearing in mind that there may be a period after the cyclone passes where there may not be power," he said.

Some supermarket shelves have already been cleared of bottled water, but they are expected to be re-stocked and further supplies will arrive before any disruption to food deliveries.

Veronica is expected to intensify as it nears the coast before weakening. ( Supplied: BOM )

Superintendent Carr warned travellers to take care around floodwaters.

"People who are travelling around that area, please do not cross flooded roadways. It is very difficult to determine the depth and how fast it is flowing," he said.

"Just because you have a vehicle that has a snorkel fitted, do not assume that you are capable of traversing that particular floodway.

"We would also encourage anyone who doesn't need to be there such as tourists to actually leave the area now.

"With the weather coming over, the storm surge and the subsequent flooding, it is not going to be a very pleasant holiday environment."

Pilbara ports cleared ahead of impact

Pilbara Ports Authority has begun cyclone preparations across the ports of Ashburton, Dampier and Port Hedland — Australia's highest tonnage port through which millions of tonnes of iron ore pass each year.

A spokeswoman said the ports were beginning to clear anchorages and berths.

Rio Tinto said the ports of Cape Lambert and Dampier were being cleared as a precautionary measure, and it too was monitoring conditions for its other operations.

Senior BOM meteorologist Andrea Peace said it could be a "dangerous period over the weekend" for the communities.

"[It is] likely to lead to significant impacts from prolonged wind, storm surge and flooding," she said.

"With very warm sea surface temperatures off the north-west coast and atmospheric conditions that are conducive to cyclone development, there's ample energy to feed this system, meaning that we can be sure that this system will intensify and gales may be experienced along the coast from Friday."

Cyclone Veronica 'textbook, very dangerous': BOM

BOM WA state manager James Ashley said it was a "textbook cyclone with a really clear eye visible on the satellite imagery".

Residents are stocking up on water and supplies ahead of the cyclone's approach. ( Supplied: Harrison Quenault )

He said it would be the first category four cyclone to cross the WA coast since Christine in 2013 and could end in a "destructive" storm surge.

"It's a very dangerous system, so bringing that system to the coast is going to bring with it really heavy rainfall and it's likely to be moving fairly slowly, which makes that rainfall even more intense over a longer period," he told ABC Radio Karratha.

"It also brings into play a storm surge with high tides across the weekend and early next week.

"Depending on the timing of the coastal crossing, there's potential for that to be very dangerous, with inundation of low-lying coastal areas.

Veronica is the second major cyclone to form off the Australian coast in recent days.

Tropical Cyclone Trevor is tracking off north Queensland and is expected to strengthen to a category four or five system as it moves west across the Gulf of Carpentaria, prompting the Northern Territory to begin the largest mass evacuation of residents since cyclone Tracy in 1974.