LONDON — Authorities in England cordoned off flooded marshes Wednesday to remove the bodies of four U.S. Air Force crewmen killed in a helicopter crash.

The Pave Hawk helicopter slammed into the eastern coast during a low-level training mission Tuesday evening. Specialist teams combing the marshes have been hampered by bullets scattered across the scene.

“We have currently cordoned off about 400 square meters (500 square yards) of the marshland area,” said Chief Superintendent Bob Scully of Norfolk Police. “The crash site itself I would describe as an area of debris on difficult terrain on the marsh.”

Local authorities are carrying out a daylight investigation, and the bodies will be removed afterward.

Pave Hawks — a modified version of the better-known Black Hawks — are mostly used for combat search and rescue missions, mainly to recover downed air crew members or other personnel during war and other hostile situations. They typically practice flying low and fast, often at altitudes of hundreds, rather than thousands, of feet.

The helicopter plummeted into the Norfolk Wildlife Trust Cley Marshes Nature Reserve. The aircraft was based at the nearby Royal Air Force station in Lakenheath.

Residents near the crash site said the helicopter sounded unusual just before the accident took place. Sue McKnespiey, who runs the Cookies crab shop in Salthouse with her husband Peter, said the helicopter came 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,” she said. “My gut instinct was there was something wrong.”

The aircraft was assigned to the 48th Fighter Wing. The names of the crew will be released after families are notified.