A woman was airlifted to hospital after her motorbike collided with a car between Erwood and Builth Wells.
The two-vehicle-crash yesterday involved the woman, aged in her 50s, who was riding a BMW motorcycle and a Ford Fiesta car.
The woman was airlifted to the Heath Hospital in Cardiff for treatment following the accident which is thought to have taken place near Erwood Bridge.
Dyfed-Powys Police, the ambulance service and the fire service all attended the A470 road traffic collision which caused the road to close.
A Welsh Ambulance Service spokesman said: "We were called at 3.18pm yesterday, Thursday 16 September to reports of a road traffic collision involving a motorcycle and a car on the A470 near Erwood, Builth Wells.
"We responded with two rapid response vehicles, one emergency ambulance and the Wales Air Ambulance. One patient was taken by air to the University Hospital Wales, Cardiff for further treatment."
It is understood that there was some queuing traffic on the A470 following the accident with drivers still being warned to avoid the area at around 6pm.
Mid and West Wales Fire and Rescue Service confirmed that while there were four casualties - including the woman - nobody was trapped in the car.
It is not yet known what condition the woman is in or what the time the road re-opened.