An investigation has begun after four crew members were killed when a US military helicopter crashed on the east coast of England during a training exercise.

A 400m area was cordoned off by police following the incident, which happened at about 6pm on Tuesday near the Norfolk village of Cley-next-the-Sea. Local people were told to stay clear.

The incident involved a HH-60 Pave Hawk helicopter, a derivative of the better-known Black Hawk aircraft, whose primary role is the transport of special forces.



View Helicopter crash, Cley, Jan 2014 in a larger map

The US air force (USAF) said that the aircraft was flying from a US airbase at RAF Lakenheath, Suffolk, south of the crash site, and had been taking part in a low-level flying exercise when it came down in marshland.

A Pentagon official in Washington later confirmed that the four crew members were presumed dead.

The aircraft was carrying munitions at the time of the crash and police said they were investigating the nature of the weaponry, which may pose a risk to the public.

Norfolk police assistant chief constable Sarah Hamlin said: "I would like to pass on my condolences to the family, friends and colleagues of those US Air Force personnel who have sadly lost their lives in this tragic incident.

A HH-60G Pave Hawk helicopter of the same type as the one that crashed in north Norfolk. Photograph: USAF/AP

"Emergency services, the military, partner agencies and volunteers have been working through the night to deal with this difficult situation on our coastline and I would also like to thank them for their professionalism and resilience.

"As our inquiry moves on today and the recovery of the aircraft begins, I would urge the public to stay away from the area – the cordon and road closures are in place to allow our experts to carry out these processes safely and there is no risk to members of the public if this section of marshland is avoided."

A second helicopter from RAF Lakenheath was also in the area at the time of the crash and set down on the marshes to try to assist. It remains at the scene while the investigation continues.

Inquiries into the cause of the crash, as well as the recovery of the wreckage and the second aircraft, are expected to take a number of days to complete, due to the geography and the munitions from the crashed helicopter. The USAF will be involved in the inquiry.

A police spokesman said that an environmental assessment would also take place.

A 400m cordon has been placed around the crash site and the A149 road through Cley is closed.

Details of the four crew members will not be released until next of kin have been informed. It is not believed that anyone in the surrounding area was injured, police said.

The base is home to the USAF's 48th Fighter Wing, also known as the Liberty Wing, which is integral to US air strength in Europe, and has been involved in anti-terrorism operations around the world.

Local reports said residents had heard F-15 planes flying over the scene of the crash, in the vicinity of a nature reserve run by Norfolk Wildlife Trust.

Dozens of emergency vehicles from the fire brigade, coastguard and police were involved in an operation at the scene on Tuesday night, while the Royal National Lifeboat Institution earlier sent out three lifeboats in response to initial reports of a crash in the area.

Peter and Sue McKnespiey, who run Cookies crab shop in the nearby village of Salthouse, live near the crash site.

She said: "We heard the helicopter come over very fast and very low. I don't know about engines, but I am used to the sound of helicopters, and this sounded very heavy and very unusual.

"My gut instinct was there was something wrong. We've now heard four people have died and it's just awful. I keep hoping the helicopter I heard isn't the one that crashed. I think the whole village will be devastated when it realises what's happened."

Helen Terry, 43, another Salthouse resident who said she had heard the helicopter flying over, said: "We assumed it was just heading out to sea for training exercises. It's a daily occurrence and we're quite used to it.

"We live less than half a mile from where it's happened and we didn't hear any bang. The first we heard was when we saw emergency crews rushing to the area."

Cley artist Rachel Lockwood, from the village's Pinkfoot gallery, said: "We had never seen so many police cars and fire engines, so went to have a look.

"The beach road to Cley is sealed off. There are lots of fire engines near the Dun Cow pub at Salthouse. A helicopter is hovering over the marsh with a light beaming down." Cley is a picturesque village one mile east of Blakeney and four miles north of Holt, on the main coast road between Wells and Sheringham.

The US military uses Pave Hawks for combat search and rescue missions during day and night, mainly to recover downed air crew or other isolated personnel such as special forces troopers operating in conflict zones.

The aircraft, which are manufactured by Sikorsky, have seen action in every major conflict involving the US since the 1989 invasion of Panama, although concerns have been expressed in recent years that their frequent use has taken a toll.

Most of the 99 helicopters in the personnel-recovery fleet have developed structural cracks due to overuse but US military budget constraints have disrupted attempts to carry out upgrades, according to a report last month in Forbes.

The 64ft-long Pave Hawk can travel at speeds of up to 184mph (159 knots) and usually carry a crew of two pilots, one flight engineer and a gunner.

All have an automatic flight control system, night vision goggles and an infrared system that enhances night low-level operations. They also have colour weather radar and an engine/rotor blade anti-ice system to help cope with adverse weather conditions. In recent years, the helicopters have been deployed in Iraq, Afghanistan and Libya.