(CNN) -- Four people are believed dead after a U.S. military helicopter crashed Tuesday near Cley, on the North Sea coast of England, authorities said.
A news release from police in Norfolk said a U.S. Air Force Pave Hawk HH-60G helicopter from a British base in Lakenheath had crashed and officials believed the four people aboard had died.
Police said a large area had been cordoned off as authorities responded. Officials are concerned there was ammunition on board, Supt. Roger Wiltshire of Norfolk Police told reporters.
The RAF base said the crash occurred during an evening training mission while the helicopter was flying low.
CNN was first alerted to reports of the crash by Twitter messages from the region.
According to the Air Force website, a Pave Hawk is a "highly modified" version of a Black Hawk helicopter that often carries a crew of two pilots, one flight engineer and one gunner.