LONDON (AP) _ A helicopter crashed Wednesday in the North Sea as it was approaching an offshore tanker loading facility, killing six people and injuring seven others, the Shell oil company said.

The accident involving a Sikorsky helicopter raised new concerns about safety in the North Sea oil fields, where there have been at least four aircraft crashes the past four years. In July 1988, 167 men were killed in an oil platform fire.

About 60 North Sea oil workers refused to fly out to the oilfields on Sikorsky helicopters until the cause of the crash has been determined.

A Shell spokesman said half the men were staying in hotels on the Shetland Islands at company expense and the rest had returned to Aberdeen, Scotland, by plane.

British Transport Secretary Cecil Parkinson told the House of Commons that the cause of the crash was not known. He said visibility was about two miles at the time and ''doesn't seem to have been a factor'' in the accident.

John Prescott, the opposition Labor Party spokesman on transport, told the House of Commons that a door had fallen off another Sikorsky helicopter on Tuesday. He did not elaborate.

The crash occurred at 10:55 a.m. as the helicopter was approaching the Brent Spar, an offshore tanker loading facility serving the four platforms in the Brent oil field operated by Shell U.K. Exploration and Production.

The helicopter, carrying 13 passengers and crew, plummeted into the water about 100 yards from the facility, Ian Henderson, Shell U.K.'s deputy managing director, told BBC Television.

The helicopter was operated by British International Helicopters, Ltd., a company chaired by British publisher Robert Maxwell, a statement from Maxwell's office said.

Rescuers in helicopters and boats, including a special diving vessel, immediately converged on the crash site, about 115 miles northeast of Lerwick, in the Shetland Islands.

Shell chairman Bob Reid told reporters at a news conference that the seven injured survivors were pulled from the water within 20 minutes after the crash.

Shell said the survivors were first ferried to a nearby company facility for treatment. One of the rescued men suffered a broken leg, Henderson said.

Parkinson said the injured were then taken to an Aberdeen hospital. He said four of the survivors were seriously hurt.

The bodies of the six victims were discovered in the wreckage by a remote- controlled mini-submarine, a Shell spokesman said.

He said the earliest the wreckage could be lifted and the bodies recovered would be Thursday.

Two of those on board were pilots, five worked for Shell and six were employed by Shell contractors, she said.

Britain's Department of Transport said it sent two inspectors to the scene to investigate.