Eyewitness described seeing a “big fireball” after the jet crashed this afternoon.
The Ministry of Defence confirmed a Hawk aircraft was involved in the accident at the Anglesey base where pilots and aircrew are trained.
Group captain Nick Tucker-Lowe said in a statement: “It’s with great sadness that the RAF can confirm the death of an engineer from the RAF aerobatics team The Red Arrows in a tragic accident today.
“The engineer’s family have been informed and have asked for a 24-hour period of grace before further details are released.
“The pilot of the aircraft survived the incident and is currently receiving medical care.”
Defence secretary Gavin Williamson said: “Our thoughts and prayers are with the family, friends and colleagues of the RAF engineer at this incredibly sad time.”
Onlookers had reported seeing someone eject from the aircraft before it hit the ground.
Caterer Anne Wilson works at The Anglesey Golf Club, situated at the end of the runway at RAF Valley, and saw the aftermath of the crash.
The 52-year-old said: “I did not see the crash, but I heard a very loud noise. We are used to the planes going over, but this was unusual.
“I did go and have a look and there was a big fireball and lots of smoke ... quite a few of the members actually saw it.
“They said the plane came in quite steeply and saw a pilot eject, but that it was very low to the ground when they ejected.”
Sian Rebecca Williams, an 18-year-old student from Rhosneigr, north Wales, said she was waiting at Rhosneigr train station when the jet flew overhead.
“The Red Arrow came over and because I’d hardly seen one before I thought ‘wow, it’s out’,” she said.
“From what I remember it did a loop and flew towards the runway and looked like it was about to land.
“As I was looking I saw the parachute of one pilot open and then the plane hit the runway with a bang and a crumbling noise.
“Then it just burned bright orange and there was smoke everywhere.”
The on-base fire engine drove out to the wreckage “instantly”, she said, putting the flames out before an air ambulance arrived.
A spokeswoman for the Welsh Ambulance Services NHS Trust confirmed an emergency ambulance and an air ambulance were sent to the scene after they were called at 1:30pm.
The world-famous aerobatic team performs stunts and daredevil displays, and fly the distinctive Hawk-fast jets.
Based at RAF Scampton in Lincolnshire, all Red Arrows pilots have flown operationally in frontline aircraft before joining the display team.
A Ministry of Defence spokesman said: “We are aware of an incident today at RAF Valley involving a Hawk aircraft..
“We are investigating the incident and it would be inappropriate to comment further at this stage.”