Eyewitnesses have revealed how they heard a “heavy and very unusual” noise as a RAF Lakenheath-based Pave Hawk aircraft crashed in north Norfolk yesterday, killing four people.

The aircraft was taking part in a low-flying exercise when it came down in a nature reserve in Cley-next-the-Sea near Salthouse at around 6pm yesterday.

Bernard Bishop, a Norfolk Wildife Trust warden based at Cley, said his house overlooks 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.”

Police have held their first press conference as specialists examine the site described as “the size of a football pitch” with bullets “scattered” around.

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

Mrs McKnespiey said: “We were watching TV at about 7pm. 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.”

Cley is one mile east of Blakeney and four miles north of Holt, on the main coast road between Wells and Sheringham.

Well-known for its windmill and church, the village has a nature reserve famous as a birdwatching site.

The area is popular with walkers and tourists, who enjoy the views and wildlife.

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.”

Richard Kelham, chairman of Cley Parish Council, said: “It looks as though the military helicopter has come down in the middle of the bird reserve. The incident is very sad.”

Helen Terry, 43, from Salthouse, said: “We heard the helicopter fly over. 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.

“It’s something locals are used to and we’ve never had any safety concerns.”

A resident who did not want to be named said: “We heard the helicopter fly over. There wasn’t any bang but soon after we heard some jets fly over very low. It was obvious it was part of a search operation and it shook our house.”