Tropical Cyclone Rusty has been upgraded to a category four, and the massive storm is now battering WA's Pilbara coast.
A red alert has been issued for people in Pilbara region towns between Pardoo and Whim Creek, including Port Hedland and South Hedland.
These residents are being told to go to shelter immediately.
The slow-travelling cyclone barely moved overnight but wind gusts have strengthened to 230km/h near its centre.
The Bureau of Meteorology predicts the cyclone will begin moving south today.
Port Hedland has already had wind gusts up 120km/h, with conditions set to worsen throughout the day, the bureau says.
Destructive wind gusts of more than 165km/h are predicted in the area as the cyclone approaches the coast.
At 5am (WST) on Wednesday, the storm was believed to be 130km north-northeast of Port Hedland and 290km northeast of Karratha.
People in communities between Wallal and Pardoo, extending inland to Marble Bar, are on yellow alert, with a warning to take action and prepare to shelter.
Rusty's massive size and slow movement is set to unleash torrential rain and cause major flooding in the De Grey catchment and significant flooding in the Fortescue catchment and Pilbara coastal streams.
The deputy mayor of Port Hedland shire, George Daccache, a resident of 40 years, expects the cyclone to be one of the worst the town has seen.
"This one's a bit of a beauty," Mr Daccache said.
"It's going to be a pain waiting for two to three days for this to come and go.
Port Hedland councillor Bill Dziombak says there's been persistent rain in the area, and he expects it will become more intense.
"This is a very long, drawn-out slow nightmare," Mr Dziombak told AAP early on Wednesday morning.
"Over the last 48 hours we've had gradually increasing gales, gusty winds and heavy, heavy rain."
The rain had softened vegetation, raising fears of falling trees and damage to infrastructure, Mr Dziombak said.
Rising tides could also cause storm surges and flooding.
Mr Daccache said most of the town's residents were at home or in shelters waiting for the cyclone to hit.
"It's in Mother Nature's hands now, nothing we can do about it," Mr Daccache told AAP.