The Mildenhall Royal Air Force base said security staff locked down the base, used by the United States military to refuel US and NATO aircraft in Europe, at about 1pm (local time) following reports of a disturbance.
"Shots were fired by American service personnel and a man has been detained with cuts and bruises and taken into custody," Suffolk police said. "No other people have been injured as a result of the incident."
Police said they were not looking for anyone else on the site after the man, a 44 year-old Briton, was arrested on suspicion of criminal trespass.
A Western security source, who spoke on condition of anonymity, told Reuters that Suffolk police were taking the lead on the incident and that specialist anti-terrorism officers were not immediately involved.
Suffolk Police confirmed in a statement they were not treating the incident as terrorism and were receiving support from other law enforcement agencies while their investigation continued.
The US Air Force said the incident at the base, which is about 125km northeast of London, had been contained and the suspect had been apprehended.
Police said they remained on the base but there was no threat to the base or local community.
Mildenhall houses the 100th Air Refueling Wing and some special operations squadrons.
The 1,162-acre base, which is home to about 3,100 US military and an additional 3,000 family members, is earmarked for closure after the United States said it was going to move its operations from the base to Germany.
The base said in a statement staff had been released from the lockdown about an hour-and-a-half after the incident.
"Individuals in the area surrounding the installation are asked to avoid the base at this time," it said.
In 2016, a delivery driver was convicted of plotting to kill US troops based in England by staging road accidents with soldiers' cars and then attacking them with knives and possibly a home-made bomb.
Prosecutors said Junead Khan had used his job to scout RAF Mildenhall and two other US bases while on carrying out deliveries.
