The pilot survived the disaster at a base in Anglesey amid reports that both he and the engineer had ejected from the Hawk aircraft.
A sign at the entrance to RAF Valley where a Red Arrows jet crashed following an incident.
An engineer has died after a Red Arrows jet crashed at RAF Valley on Anglesey.
"'We are investigating the incident and it would be inappropriate to comment further at this stage".
She said: "The Red Arrow came over and because I'd hardly seen one before I thought "Wow, it's out". Then it looked like it was about to land, then next thing I saw was the parachute and then the plane hit the runway and went up in flames".
An air ambulance has been scrambled to RAF Valley to assist the emergency services already on scene.
The RAF is asking eyewitnesses with photographs of the incident to send them in to help with the investigation and not share them online.
The 52-year-old told Independent.ie: "I did not see the crash but I heard a very loud noise".
The Hawk fast jet has been left destroyed by the crash, and the condition of the two people on board is still unknown.
The Ministry of Defence has tweeted that the engineer's family have been informed.
"The pilot of the aircraft survived the incident and is now receiving medical care".
Chief Inspector Simon Barrasford at North Wales Police, who is leading the initial response, said: "The aircraft involved, a Red Arrows Hawk crewed by two RAF personnel, was reported to have crashed".