Boat off WA being handled by police

A suspected asylum seeker boat off Western Australia's north coast is being handled by state police before the navy takes over, Premier Colin Barnett says.

A spokesman for oil and gas sector contractor MODEC said on Monday the boat was spotted off Dampier by workers on a tanker.

It had entered the 500-metre exclusion zone around an oil rig, some 140km off the coast.

Mr Barnett said it was always concerning when asylum seeker boats got close to shore, but the matter was under control.

"The West Australian police is looking after that situation until the Commonwealth naval vessel arrives, so the situation is in order," he told reporters.

"This boat, while it's approaching our coast, it's well offshore and it's under surveillance."

It had been reported that the Australian Maritime Safety Authority would fly out to assess the situation, but AMSA declined to comment.

The Department of Immigration and Border Protection referred questions to Immigration Minister Peter Dutton, but his spokeswoman said it was a long-standing policy that the government did not comment on operational matters.

Two years ago, a group of Vietnamese asylum seekers in a wooden boat came near a floating LNG production and storage vessel off Dampier.

Mr Barnett also expressed concern about that incident at the time, saying he understood the boat had been tied up to the floating platform. But Customs denied this, saying the asylum seekers had only waved at workers on the vessel.

They were sent to Christmas Island.