A suspected asylum seeker boat has been spotted off Dampier in Western Australia's North West region.

A Federal Government source has confirmed to the ABC a boat was sighted and will be intercepted.

The ABC understands the boat could be carrying asylum seekers from Vietnam.

A spokesperson for oil and gas company Modec confirmed crew members on one of their tankers off Dampier sighted what appeared to be an asylum seeker boat at first light this morning.

Numbers could not be confirmed but the spokesperson said those onboard appeared to be in good health.

The ABC understands the North West-based police boat Delphinus has been deployed to search for the suspected asylum seeker boat.

The police vessel had been involved in the search for three missing fishermen and their vessel off the Dampier coast until this morning.

Police have been told the suspected asylum seeker boat was believed to be about 70 kilometres offshore.

The Australian Maritime Safety Authority (AMSA) said it could not comment on the sighting.

A spokesperson for Minister for Immigration and Border Protection Peter Dutton said the Government did not comment on operational matters.

The Greens have criticised the level of government secrecy surrounding the boat's arrival.

"There's no justification for the minister and the department to keep the Australian people and the Australian Parliament in the dark," Greens senator Sarah Hanson-Young said.

"Be upfront about what has occurred here, and just have the guts to tell the Australian people what indeed is going on at our borders."

WA Premier Colin Barnett said he believed West Australian police were "looking after the situation" until a Commonwealth naval vessel arrived.

"This boat while I think it's approaching our coast is still well offshore and it's under surveillance," he said.

"So the situation is in order.

"I think the Abbott Government is doing an enormous amount and has stopped the arrival of boats."

It is almost two years to the day since an asylum seeker vessel arrived at a floating oil platform 200 kilometres off Dampier with 17 people from Vietnam on board.