The HH-60G Pave Hawk, assigned to the 48th Fighter Wing at RAF Lakenheath, went down near the village of Cley Next The Sea in Norfolk County, the Air Force Times reported. The British air station said the crash occurred during a training mission.
While an Air Force official said the condition of the four crew members was unknown, Norfolk County police told local media all four were killed, the Times said.
The British newspaper the Daily Telegraph reported a Norfolk police spokesman said in a statement: "Police are currently dealing with a single helicopter crash in the Cley area on the north Norfolk [County] coast. There are believed to be four dead. Officers are on the scene."
Britain's Ministry of Defense said it was investigating the reports, but had no details, the Telegraph said.
The fire service earlier said it was called about an aircraft crash in the nearby village of Salthouse, but said it was a false alarm, the Telegraph reported.