A US Air Force (USAF) military aircraft has damaged a hospital helipad during a training exercise, leaving it temporarily unavailable to air ambulances.
Addenbrooke's Hospital in Cambridge is the East of England's major trauma centre.
Patients are instead currently being flown to Cambridge City Airport where one of the East Anglian Air Ambulance (EAAA) teams is based.
They have to complete the last part of their journey to the hospital by land ambulance with critical care staff on board.
Up to 800 people receive major traumatic injuries each year in the East of England.
The helipad was damaged by a USAF CV-22B Osprey tiltrotor aircraft.
A video reportedly from the incident shows parts of the helipad blowing up from the ground as the aircraft took off from it on Wednesday.
Repair work on the helipad at Addenbrooke’s Hospital, which is used by the region's three air ambulances, is under way.
Dr Victor Inyang, Medical Director of the EAAA, said: "Addenbrooke's is the major trauma centre for the region, therefore quick and efficient transfer of critically ill or injured patients to the hospital is vital.
"Using the EAAA helipad is the best alternative while the CUH [Cambridge University Hospitals] helipad is reinstated.
"The situation has been handled incredibly well by all parties involved and we are optimistic that the helipad will be back in use very soon."
Watch: A video posted online reportedly shows the incident of the helipad being damaged.
The USAF Osprey aircraft can take off, land and hover like a helicopter, and when the position of its rotors are tilted it has the long-range efficiency and speed of a turboprop aircraft.
Major Keavy Rake, of USAF’s 48th Fighter Wing, said: "The area was surveyed according to our policies and procedures and some damage did occur.
"We are taking steps to rectify as soon as possible.
"Our units are continuously coordinating with our local partners to improve operations.
"We are greatly appreciative of the relationship and coordination we have with the UK."
A spokesman for Cambridge University Hospitals NHS Trust said: "While our normal helipad is being repaired air ambulances will temporarily land at nearby Cambridge City Airport and patients are then transferred to the hospital in road ambulances with critical care staff on board, meaning we can continue to see and treat them as normal."