Craft from US base at RAF Lakenheath goes down on low-level mission, scattering live ammunition over marshes

Police investigating a US helicopter crash on the Norfolk coast that killed four crew members and scattered live ammunition over a nature reserve said the incident occurred during a training exercise involving a second US helicopter.

Chief Superintendent Bob Scully, of Norfolk police, said the aircraft were HH-60 Pave Hawk helicopters. Speaking on Wednesday at a press conference at the scene, in the village of Cley-next-the-Sea, he said the second helicopter was not thought to have caused the crash.

But he added it was too early to speculate. "The two aircraft were involved in some training activity," Scully said.

"The most immediate aircraft to provide assistance was the other aircraft. It will be a matter for the [air] investigation to establish whether there was any causal link. My understanding was apparently not but we don't know. We should allow them to carry out the full investigation."

The wreckage of the crashed US helicopter lies near the beach at Cley-next-the-Sea. Photograph: Chris Radburn/PA

At later press conference he suggested the investigation was taking no longer than expected. The coroner, Jacqueline Lake, who examined the bodies has given permission for them to be moved, but this is not now expected to take place until Thursday.

Scully said: "Removal of casualties from the aircraft can disrupt the evidence, so it has to be done methodically step by step. So it will take some time to remove the deceased from the aircraft, possibly until tomorrow."

Responsibility for the crash site is also likely to be formally handed over from Norfolk police to US and UK military air investigators on Thursday. The police had hoped to complete the handover on Wednesday.

Helicopter crash site.

The aircraft had flown from the US airbase at RAF Lakenheath in Suffolk before the crash.

A spokesman for the base said the names of the crew would not be released until 24 hours after their families had been informed.

Tributes were paid to the deceased during prime minister's questions in the Commons. Both David Cameron and the Labour leader, Ed Miliband, expressed their condolences to their families.

The crash site, on "difficult terrain in the marsh", was scattered with live ammunition and would remain cordoned off for several days, Scully added.

Police at a roadblock at Salthouse. Photograph: Chris Radburn/PA

The A149 between Cromer and Hunstanton, which runs alongside the crash site, is likely to remain closed until Monday. Cley Marshes nature reserve has been closed and will remain shut on Thursday.

Scully said: "The crashed aircraft did contain ammunition. That ammunition is not of any great significance – it is bullets, if you will – but those are scattered about the site, so the site is hazardous to members of the public and those people that would normally visit this area for birdwatching and other nature-interest activities. So we will be working with the military to ensure public safety by restricting access to that area.

HH-60 Pave Hawks flying over RAF Lakenheath. Photograph: US Air Force/RAF/PA

"The debris is not on the beach but there are some bits of debris that are vulnerable to high tide. The majority of the debris is on the marsh."

He added that the crash investigation was likely to take some time, urging the public to be patient.

A statement from the US air force's 48th Fighter Wing, based at RAF Lakenheath, said: "US military officials are co-ordinating the recovery efforts with the UK police and the Ministry of Defence.

"The aircraft, assigned to the 48th Fighter Wing, was performing a low-level training mission along the coast when the crash occurred."

A US military helicopter that landed at Salthouse, near the crash scene. Photograph: Chris Radburn/PA

A spokesman added that the RAF understood the crash had happened at 6pm on Tuesday.

Residents spoke of hearing a "heavy and very unusual" sound overhead before the helicopter, which specialises in recovering troops from war zones, hit marshland at the Norfolk Wildlife Trust's Cley Marshes nature reserve.

Police said no one in the surrounding area had been injured.

Bernard Bishop, a Norfolk Wildlife Trust warden based at Cley, said his house overlooked the crash site and he had never seen anything like it.

"I heard the helicopter flying overhead and watched from my back garden," he said. "It was very quickly obvious something serious was wrong. The search-and-rescue crews quickly arrived and it was my job to escort them over the marsh.

"The conditions are very difficult because the marsh has flooded twice in recent weeks, so that's hampering their efforts to recover the bodies and make the helicopter safe.

"There's only one track in and out of the crash site, which is also restricting their movements. It's just awful. I've never known anything like and never seen so many people here at one time."

Other residents said there had been longstanding concerns about the low flying training exercises in the area.

Richard Howitt, the Labour MEP for the area, said aerial training exercises did cause disruption but were accepted by the community. Speaking to BBC News he said: "It is one of the most wild and tranquil places in which to be. Of course those training exercises bring some noise and disruption but most of us from the local community welcome that. They know they are doing a job on our behalf in defence of our country. It's something that it is accepted.

"Cley Marshes are the jewel in the crown of the Norfolk Wildlife Trust. Many people who have walked that north Norfolk coastal path know about the wonderful marshes and beaches, and will understandably be concerned that live ammunition is there."

Matthew Hancock, MP for West Suffolk, which includes Lakenheath, said: "Lakenheath is a close-knit community, and I know that this tragic loss of life will be deeply felt.

"In Suffolk we never forget that the presence of the men and women of the 48th Fighter Wing helps guarantee Britain's security and shared freedoms. This crash reminds us of the bravery of our allies, in training and in war."