Investigations have started into what caused a US Air Force helicopter to crash in Norfolk, killing all four people on board.
The HH-60G Pave Hawk, based at RAF Lakenheath in Suffolk, came down at a nature reserve in Cley next the Sea on Tuesday night.
The aircraft, from the 48th Fighter Wing, was on a low-level training mission and carrying live ammunition.
A 1,200ft (400m) area is cordoned off and the A149 through Cley is closed.
The wreckage, including a "significant" number of bullets from the crashed aircraft, is scattered over an area the size of a football pitch, police said.
The US Airforce says the helicopter was on a low-level training mission when it crashed. It would have been flying in a pair, probably on a dusk to night-time flight.
Such training missions give the crew the hours they need to keep up their night-flying to remain combat ready. They would normally fly the same mission in the day to familiarise the route.
A US Airforce spokesperson said it would have been normal for the downed helicopter to be carrying ammunition for its machine guns on a training mission. It's not yet clear whether the crew had been, or were about to use those weapons.
What we do know is that US Airforce Pave Hawk helicopters have been using RAF Holbeach - a remote weapons range on the Lincolnshire coast, about 18 miles west of King's Lynn - over the past few days.
It will take a number of days to carry out an inquiry, due to the geography of the area and the live munitions.
The public are urged to avoid the site, which lies in marshland between the A149 and the coastline, while emergency services, Ministry of Defence, US Air Force and HM Coroner assess the site.
A second helicopter from RAF Lakenheath, which landed on the marshes shortly after the crash also remains at the scene.
A large military lorry, loaded with an excavator and what looked like a battery unit has driven to the crash site, BBC reporter Simon Newton said.
Ch Supt Bob Scully, from Norfolk Police, said officers received reports of a helicopter crash "somewhere on the north Norfolk coast" at about 19:00 GMT, and quickly established it was at Cley. He said the inquiry was being led by police "in situ", with the bodies of the four crew members to be recovered once initial investigations had taken place.
"The crash site is about the size of a football pitch, with difficult terrain which makes this a challenging and lengthy process," he added.
"This is mainly on marshland although some debris which was close to the beach has been moved as it would be vulnerable to high tide. ..."More from BBC News