A crash between Llanbister and Llanddewi has caused the A483 to close in both directions.
The collision, which happened at around 10.40am today, happened on the stretch of road between the B4356 and Dan-Y-Gaer.
Police, the Welsh Ambulance Service and the fire service are at the scene of the crash near Llanbadarn Fynydd and the road is closed to allow the air ambulance to attend.
Drivers in the area have been warned to expect delays and road diversions are in place.
The Mid and West Wales Fire and Rescue Service tweeted at 11.24am: “Crews from Llandrindod Wells are in attendance at an RTC on the A483 junction with the B4356 at Llanbadarn Fynydd.
“Dyfed-Powys Police, the Welsh Ambulance Service and Air Ambulance are on scene. Delays in the area whilst emergency services deal with the incident.”
A Welsh Ambulance spokeswoman said at 12.30pm: "We were called on Monday 12 August at approximately 10:04 am to reports of a road traffic accident involving two vehicles near Llanbister.
We responded with one emergency ambulance and we were supported by the Wales Air Ambulance. One patient was treated at the scene.”
A Mid and West Wales Fire and Rescue Service spokesman said crews from Llandrindod Wells had attended at 10.46am.
He said:"A male driver extricated himself from one of the vehicles whilst a male casualty in the second vehicle was medically trapped and removed by firefighters and paramedics.
The Air Ambulance, Ambulance Service, Police and Highway Agency were also in attendance.
Firefighters made safe the vehicles using a fuelled saw, winch, hose reel jet, small gear and an environmental agency pack.The Fire Service left the incident at 12:36pm.