A Norwegian oil rig support ship carrying 14 people capsized off northern Scotland on Thursday, and six crew members were missing, the coast guard said.

Eight were rescued from the vessel, which capsized off the northern tip of Shetland Island, said Mark Clark, a coast guard spokesman.

Two coast guard helicopters and three offshore vessels raced to the scene.

"We've issued a mayday call for any vessels in the area to come to us immediately because we need divers. If those six guys are trapped underneath the hull, we need to get to them," Clark said in a telephone interview.