Shots were fired by US service personnel and a man has been detained after a disturbance at RAF Mildenhall, Suffolk Police said.
Police are responding to reports of a "significant incident" at RAF Mildenhall.
The US Air Force base in Suffolk is reportedly on lockdown amid reports of a car trying to ram the gates.
A brief statement on the base's Facebook page said: "RAF Mildenhall locked down at 1pm today following reports of a disturbance on base.
"The base was locked down and emergency personnel are responding to the situation.
In a statement Suffolk Police said..
"Police are continuing to deal with an ongoing incident at RAF Mildenhall, it is considered that there is no wider threat to the public or occupants on the base.
One man has been arrested and police are not looking for anyone else on the site."