Severe Tropical Cyclone Ilsa crossed the coast near Port Hedland just before midnight (17:00 BST) on Thursday as a category five storm.
It has since been downgraded to category four but still has the potential to cause significant damage.
A red alert was issued hours earlier, with thousands of people ordered to take immediate shelter.
It is the country's most serious cyclone alert level. Under it, people are told to remain in the strongest, safest part of their homes and to stay away from doors and windows until they are given the all clear by authorities.
While northern Australia is no stranger to cyclones, this storm is the strongest to hit the region in 14 years.
The "very destructive core" of the storm will bring "extreme" wind gusts of up to 315km/h (195mph) in parts of the Kimberley and Pilbara regions, the Bureau of Meteorology (BOM) said.
Winds of 218km/h were recorded on Bedout Island just off the coast as the storm touched down, setting a preliminary 10-minute sustained wind record, according to the BOM.
The previous record was 194km/h - winds that were recorded when Cyclone George hit Australia in 2007.
"There is a threat to lives and homes. You are in danger and need to act immediately," the Department of Fire and Emergency Services said, when the red alert was issued on Thursday afternoon, local time.
Residents, including some 15,000 people in Port Hedland, the world's biggest iron ore exporting port, have been ordered to shelter inside and stay away from doors and windows.
"It is too late to leave. Stay indoors until the all clear is given by authorities," the red alert warning states.
Port Hedland Mayor Peter Carter said evacuation centres had been set up in the town.
"Everyone is on edge," Mr Carter told the Australian Broadcasting Corporation. "They understand that cyclones are what they are. They're very, very unpredictable."
On Thursday as the cyclone approached, residents made last minute preparations by sandbagging and securing homes and businesses, Channel Nine reporter Ezra Holt told the BBC from Port Hedland.
He added that there were mixed emotions within the town, with some not too fussed, and others more concerned because cyclones this strong are quite rare.
Weather officials also warned of up to 400mm (15.7in) of rain and abnormally high tides, with the storm's impact felt across a 600km (370 mile) region from Port Hedland to just south of Broome.
Some 700 residents from the remote community of Bidyadanga have been evacuated, the fire service has said.