A US F-18 jet has crashed near RAF Lakenheath in Suffolk, sources confirmed.
It is not known if there are any fatalities following the incident, on farmland near the military base.
Emergency services were sent to the scene near the Cambridgeshire/Suffolk border.
A Cambridgeshire Police spokesman said: "We are currently at the scene of a plane crash on farmland in Redmere, Ely.
"Details are sketchy at this stage and it is not known if there are any casualties.
"As and when more information becomes available we will let you know."
A source told the Press Association the crash involved an US Navy F-18 single-seat aircraft.