Police officers have been called to Northampton Magistrates Court after an altercation in the waiting area
The clash, believed to be between two rival gangs started at about 11.30am.
Police dispersed the gangs in the waiting room but ushers were forced to lock staff, solicitors and members of the public inside the courtrooms for their own safety.
A witness who was shut in a courtroom said he could hear people shouting and throwing things at each other, perhaps cans of drink.
Another said the altercation involved more than 20 people.
People in the court were told by officials that armed response police officers were outside to deal with incident.
UPDATE: A police spokeswoman confirmed armed officers who were nearby were called to the court, and the people involved in the incident dispersed.