The A465 is closed between the B4347 to Hay-on-Wye and The Old Pandy Inn.
Emergency services were called to the main road at just before 2pm after receiving reports of a lorry crashing into a building.
Images seen by Sunshine Radio show a large impact to the front of a house after being smashed into by a lorry carrying tree logs.
Fire crews from Abergavenny and Ewyas Harold are in attendance along with the ambulance service.
A spokesman for Gwent Police said: "Emergency services are dealing with a road traffic collision on the A465 Hereford to Abergavenny.
"The road is closed and diversions are in place which may cause congestion.
"Please avoid the area if possible and find alternative routes for your journey."
A Welsh Ambulance Service spokesperson said: "We were called today at 1.29pm to reports of a road traffic collision involving a lorry in Llangua, Abergavenny.
"We attended scene with two rapid response vehicles and one emergency ambulance.
"One person was taken to University Hospital Wales, Cardiff for further treatment."
The road is expected to remain closed for several hours.