Tropical Cyclone Rusty is continuing to intensify as it tracks directly towards the stretch of coast in Western Australia known as 'cyclone alley'.
At last report, the category two system was 250 kilometres north of Port Hedland and nearly stationary.
It is is still more than a day away from making landfall along the Pilbara coast but by then it is expected to have intensified to a category four system.
The Bureau of Meteorology's Mike Bergin says its slow moving nature will result in very heavy rainfall with dangerous and destructive winds.
"At the moment we're facing the evolution of an extremely dangerous event," he said.
Earlier, the bureau's Andrew Burton says it is likely to cross near Port Hedland.
"The most likely outcome is that we end up with a very large, very intense tropical cyclone, moving slowly producing a lot of rain, a long period of destructive winds," he said.
"Basically, it really is a corker of a storm that we really need to be very prepared for."
The bureau is expecting wind gusts well in excess of 200 kilometres per hour near the centre of the cyclone, maybe heading up towards 250 kilometres per hour.
Both Port Hedland and Karratha could be affected.
The Department of Fire and Emergency Services' Phil Cribb is urging residents to take care.
"Heed the advice, make sure you stay inside and once we go past the cyclone, make sure you don't go out too early," he said.
There is a yellow alert for communities between Walla and Whim Creek, including Port Hedland, De Grey and Pardoo.
A blue alert has been issued between Cape Leveque and Wallal, including Karratha.
Residents are being told to organise emergency kits including first aid kit, torch, portable radio, spare batteries, food and water.
David Harding, the Port Hedland Woolworths manager, says people have been stocking up and his store had about 50 percent more trade than a normal on the weekend.
"Bulk water, whether it be the 24 packs or the big large containers, also long life milk, any canned fruit, veggies, all the tinned stuff," he said.
Port Hedland's deputy mayor, George Daccache, says the threat is understood.
"I would say the majority of the town is prepared but there's nothing like spreading the word even more now that there is a real threat that this could possibly be a major hit by a cyclone," he said.
The town's CEO Mal Osborne says evacuation centres have been set up.
"The town is busy preparing itself to ensure that in the first instance that welfare centres are available for the Department of Community Protection, Child Protection, to run as welfare centres for evacuation requirements," he said.
"We wait for SES to advise us they want to open those centres and DCP then run the facilities."
Mr Osborne says time is running out for homeowners and construction workers in the town to make their properties safe.
"We are imploring people, whether it's their own home, their own backyards, or whether they have a development site, to actually do the best they can to make those sites as safe as they can," he said.
Schools in the Pilbara will be closed until further notice.
The Port Hedland port has been closed as has the airport.
Apache is evacuating non-essential personnel from offshore operations in the area while Woodside says is taking the necessary precautions to safeguard its people and assets.
BHP says it is making appropriate preparations to ensure the safety of employees.
Rusty has already delivered a lot of rain along the Kimberley coast, with some cattle stations recording more than 250 millimetres within 24 hours.
The bureau says very heavy rainfall is expected near coastal parts of the eastern Pilbara and western Kimberley today, with widespread falls tomorrow and Wednesday likely to lead to major flooding in the De Grey catchment.
The bureau says significant flooding in the Fortescue is also likely.
The State Emergency Services says road access has been cut to some Aboriginal communities but so far all are faring well.
SES district officer Matt Reimer says they are keeping in contact with pastoral stations and remote Aboriginal communities.
He says extra crews from the metropolitan area will be deployed to Karratha and Port Hedland today to assist local emergency staff.
"It's likely they will be operating on a 24/7 basis so they will require some additional staff to cover those shifts," he said.
Meanwhile, more than 775 millimetres of rain has been dumped on the Cocos Islands in a downpour which is the equivalent of Perth's annual total rainfall in just three days.
The bureau says the tropical low which brought the rain could develop into a cyclone in the next few days.
© ABC 2013
19:53 EDT Wind gusts of up to 90 kilometres an hour brought down power lines, cut traffic lights and delayed public transport across Sydney this afternoon.