Police were first called to the incident at the village of Gillingham, near Beccles and Lowestoft, at about 7.30pm on Thursday night.
A few hours later, the East of England Ambulance Service (EEAST) said it believed that all the occupant’s had died.
Police confirmed that the aircraft was civilian rather than military, and that the area of the crash site has been cordoned off.
A spokesman for EEAST said: "Sadly, it is believed that four people in the helicopter are believed to have died in the crash. Ambulance resources have now been stood down from the scene. Our thoughts are with the family and friends of those who have lost their lives tonight."
"EEAST sent a number of resources to the incident including two ambulance officers, three ambulances, two doctors and one rapid response car."
One Twitter user said that the helicopter came down near his house, which he wrote was near the woodland leading to the small village of Gillingham.
A screengrab taken from Sky News showiong the area in which a helicopter crashed on Thursday evening A screengrab taken from Sky News showing the area in which a helicopter crashed on Thursday evening. Photograph: Sky News
Roland Bronk, owner of The Swan House inn and restaurant in Beccles, said it was "very foggy" in the area. Bronk said he also heard customers talk about "a lot of police activity and ambulances".
It is not yet known whether fog, which beset much of England earlier in the day, played a factor in the crash, although the visibility was reported to be poor in the area on Thursday night.
The site is 45 miles from the spot where four crew members died when a US military helicopter crashed in January on a training mission in a nature reserve in Cley-next-the-Sea.
All four American crew members were killed in the crash. Residents described hearing a "heavy and very unusual" noise from the helicopter seconds before the crash.
The aircraft was carrying munitions at the time of the crash and police subsequently cordoned off the area as they investigated the nature of the weaponry, which was later found to be bullets.