Two pilots ejected and parachuted out of their plane before a crash involving an RAF training aircraft.
North Wales Police said the pilots of the RAF T2 Hawk aircraft were being treated for minor injuries following the incident in the Pencarnisiog area of Anglesey.
The force said helicopters from the Coastguard and the Wales Air Ambulance were at the scene close to RAF Valley on the island.
“Two pilots are being treated for what are thought to be minor injuries and at this stage there are no reports of any wider damage or injuries,” it said.
“Please avoid the area until further notice.”
The Ministry of Defence has been asked to comment.
The Royal Air Force said: “An incident involving an RAF T2 Hawk aircraft, flying out of RAF Valley.
“An investigation is under way and we will not comment further at this time.”