The crash involved a US military helicopter which came down on a flooded area of land near the beach car park in the town of Cley-next-the-Sea.
Police last night confirmed the dead were all Air Force crew members.
The helicopter was a US Pave Hawk that had been based at nearby RAF Lakenheath in Suffolk.
Police cordoned off a 400-metre area and urged local people to stay well clear of the crash site.
A spokesman for Norfolk Police said: “We are dealing with a single helicopter crash in the Cley area, on the North Norfolk coast.”
The 48th Air Wing of the US Air Force based at RAF Lakenheath tweeted: “We can confirm that one of our HH-60G Pave Hawk helicopters was involved in an
incident during a training
mission outside Cley-Next-The-Sea.”
The accident scene is between Cley beach car park and Eastbank, near Salthouse, an area which remains flooded following the recent tidal surge.
Some residents had reported hearing F-15 aircraft searching overhead.
Cley artist Rachel Lockwood, from the village’s Pinkfoot Gallery, said: “We had never seen so many
police cars and fire engines.
“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. Well known for its windmill and church, the village has a nature reserve famous as a birdwatching site.
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.”