Six people were arrested after about 100 people were discovered in a former pig shed at an unlicensed music event.
Norfolk Police said it was called just before midnight on Saturday by a member of the public who said they had seen suspicious activity on land by Mundford Road, Methwold.
Officers arrived at about 04:00 BST on Sunday and found music "being played intermittently".
They closed entrances and seized vehicles and equipment.
The force said officers monitored the event "throughout the early hours of the morning" and placed police vehicles to stop more people from entering.
Two men in their 30s, a boy in his late teens, and a man and woman in their 20s were arrested.
The woman was released under investigation and the remaining suspects were released on police bail until 30 June.
Another man in his 20s, from Cambridgeshire, was arrested at the scene for breaching a court order.
He was remanded into custody to appear in court at a later date, police said.