The two-vehicle collision happened on the A470 Newtown to Llanidloes Road at Llandinam, closing the busy tourist route for several hours.
Emergency services were called to the scene at about 1.50pm.
Dyfed Powys Police closed the road while the fire service and ambulance crews worked together at the scebe.
A Welsh Air Ambulance helicopter landed in the field alongside the main road.
A spokesman for Wales Ambulance Service said "We responded with one emergency ambulance, one rapid response car, our Emergency Medical Retrieval and Transfer Service plus the Wales Air Ambulance.
"We assisted colleagues from the fire service on scene and one patient was taken by air to the Royal Stoke University Hospital for treatment."
Long queues of traffic built up stretching almost to Newtown and police said there was congestion on other, smaller roads as motorists tried to find other routes around the crash.