The 6.6 magnitude undersea quake struck at 3.39pm AEST on Sunday between Port Hedland and Broome, GeoScience Australia reported.

"As it stands for as long as today, it is the biggest-equal earthquake in Australia ever recorded," GeoScience Australia duty seismologist Dan Connolly said.

It equalled the magnitude of an earthquake recorded in Tennant Creek, Northern Territory, in 1988.

The government agency first reported it at 5.5 magnitude before boosting it up.

The United States Geological Survey said the quake hit at a depth of 33km, about 203km offshore. It reported the magnitude at 6.9.

"An earthquake of this size ... the enormous size, it was felt up to Darwin and down to Perth. It is a rare occurrence," Mr Connolly said.

There is no threat of a tsunami to the Australian mainland, islands or territories, the weather bureau said.

There have been at least four aftershocks following the earthquake, ranging from 3.8 to 5.2 magnitude the agency reported.

Mr Connolly said more aftershocks were expected to flow and that was "absolutely normal" but he could not predict where, when and what size they would be.

Derby resident Jody Gaunt was having a beer with friends when they felt the quake.

"We were sitting outside and our chairs were rocking," she said.

"The trees stopped moving and the breeze stopped blowing.

"We were thinking, 'Is this real or not real?' We've never had an earthquake up here, or a tremor."

Ms Gaunt, 53, said the quake was the talk of the neighbourhood and it was reported that items had been shaken off the shelves at the local Woolworths.

In Port Hedland, The Walkabout Hotel employee Shelley said it felt like being on a vibrating machine.

"It felt like being on one of those vibrating machines. It just sort of shook the building," she said, adding a colleague thought it was a jet from the neighbouring international airport taking off.

The Roey Hotel employee Cindy said she saw cars moving in the earthquake.

"I was outside and I just saw the cars moving. It was a bit scary. You could see them moving. A few things fell off the walls onto the floors," she said.

"It just went for a few seconds."

Gary, who works at the Mercure Hotel in Broome, said it started as a little shake before the doors and walls rattled and it "developed into quite a shake".

"It was quite nerve-racking. It was not too strong, it almost felt like when you are in a car and the wind is a bit strong, and then it started picking up," he said.

Deb Hannagan, from Broome, tweeted: "We just had an earthquake in Broome! The whole house was shaking and it went for ages. Never experienced anything like it before - quite amazing!"

A St John Ambulance spokeswoman, who said she felt the quake in Perth, said there had been no injuries reported.

It is also understood there has been no building damage, according to a police spokesman.