OSLO -- A helicopter ferrying passengers from a Norwegian oil platform crashed in the North Sea on Friday, killing at least 11 of the 13 people on board, rescue officials said.
The 11 passengers and two crew on the flight from the Gullfaks B oil platform, operated by Statoil, were all Norwegian except for one British and one Italian national, according to the Rescue Coordination Centre for Southern Norway.
"The helicopter is completely destroyed," it said. After several hours searching for survivors, 11 bodies were found and the remaining two people were presumed dead.
Several witnesses told Norwegian media they saw the rotor separate from the helicopter while still in the air.
"While I looked up, the rotor loosened and disappeared toward the north," John Atle Sekkingstad told the website of local paper Bergens Tidende.
"After that, the helicopter turned north and I saw fire at the top of the helicopter, where the rotor had been attached. It caught fire before it crashed."
The main body of the aircraft was lying under water, while its rotor was found on a rocky outcrop 200-300 meters (yards) away, state broadcaster NRK said, quoting the rescue center.
Plumes of smoke rose from the scene, a stretch of sea with many small islands. Pieces of red debris could be seen on the rocks, TV pictures showed.
Another witness, oil worker Chris Andersen, told NRK: "I saw the rotor separate .... It was horrible. There was a huge explosion that you could physically feel. You felt the vibrations."
Norway's king and the prime minister expressed their condolences to the families of the victims.
"You are not alone in your sorrow," Prime Minister Erna Solberg, dressed in black, said in an address to the nation.
The site of the crash, just west of Bergen, Norway's second-largest city, has frequent helicopter traffic to and from offshore oil installations. Weather conditions on the day were normal.
The Norwegian Civil Aviation Authority immediately imposed a temporary flying ban on type of helicopter involved, a Eurocopter EC225LP, but said it was too early to say anything about the cause of the crash.
The flight was operated by CHC Helicopter, owned by U.S. private equity firm First Reserve, it said.
Airbus Helicopters, a subsidiary of Airbus Group, which is what Eurocopter is now known as, said it was "deeply saddened by this tragedy" and expressed its sympathy for the victims and their loved ones.
"Safety is Airbus Helicopters' top priority and we are providing our full support to both the accident investigators as well as CHC. Airbus Helicopters teams are fully mobilized to understand the root cause of the accident."
Now known as the H225 Super Puma, the aircraft is a long-range helicopter widely used in the oil and gas industry.
The company's website says it "has accumulated more than 4.3 million flight hours during operations around the world and in all weather conditions, including highly challenging maritime environments."
The aviation authority said there had been problems with the helicopter model in 2012 "when errors in the main gear box were identified" but that the manufacturer had since produced a modification that was approved by the European Aviation Safety Agency. Airbus did not comment on that.
(Additional reporting by Terje Solsvik and Nerijus Adomaitis.)