One of Yorkshire's two air ambulances has been grounded while medical staff are redeployed back to emergency medicine and ambulance roles.
Yorkshire Air Ambulance will now be operating only one helicopter from its base near Wakefield.
All the air ambulance doctors are going back to roles in emergency medicine, anaesthesia and critical care.
The service said the move was because of the "unprecedented crisis" of coronavirus.
The remaining helicopter will be manned by two critical care paramedics and a pilot.
Peter Sunderland, chairman of Yorkshire Air Ambulance, said a "small number of the highly skilled critical care paramedics will be deployed to support the road ambulance crews".
He also urged people to stay at home to minimise pressure on the service.
He said: "Yorkshire Air Ambulance wants to do everything it can to support the NHS and Yorkshire Ambulance Service in their fight against Covid-19. It is important that everyone does their part, including us.
"We would also strongly reinforce the government's message to stay at home during this crisis.
"Travelling further afield in cars to places like forests or moorlands can increase the risk of possible unnecessary accidents such as road traffic collisions or falls where our services might be required.
"With a reduced service currently available, it's vitally important we are available for the most urgent cases."
The service will continue to operate daily from 07:00 to 19:00 BST.