The civilian craft crashed in Gillingham, near Beccles, on the Suffolk border, at 7.30pm tonight.
A spokeswoman for East of England Ambulance Service said: "We got called to reports of a helicopter crash near Beccles and we sent several resources to the scene, including doctors."
Reports suggested a civilian helicopter made by Anglo-Italian firm AgustaWestland was involved, not a military aircraft.
It was unclear from initial reports how many people were on board.
It is also not immediately known whether fog, which beset much of England earlier in the day, played a factor in the crash.
Roland Bronk, owner of The Swan House inn and restaurant in Beccles, said it was "very foggy" in the area.
Mr Bronk said he also heard customers talk about "a lot of police activity and ambulances".
The accident site is just 45 miles from Cley Next The Sea, where four US airmen were killed in January when their Pave Hawk military helicopter came down in a marsh.
The helicopter from RAF Lakenheath was taking part in a low-flying training exercise.