Police in Suffolk are responding to a "significant incident" at Suffolk RAF Mildenhall.
The US arirfoce base is in lockdown while police attend the scene.
In a tweet, Suffolk Police said: "Police are responding to reports of a significant incident at RAF Mildenhall, further details shortly."
The main incident is thought to be over, after it was reported that someone attempted to ram their vehicle past a checkpoint.
An MoD spokesman said: "We are aware of incident at the entry point of RAF Mildenhall, Suffolk police have primacy; all questions should be referred to them."
The individual has been arrested and is now in the custody of Suffolk Police.
Members of the public have been asked to avoid the area while police carry out further checks.
The lockdown ended shortly after the driver of the vehicle was arrested.
Mildenhall was one airbase that was a potential target by a British-born Islamic State supporter who was jailed for life in 2016.
The airbase, which first opened in 1934 close to Suffolk, is currently operated by the US Air Force.
In 2016, the Ministry of Defence announced that they would be selling the airfield along with a series of other bases.