An air ambulance was called to a serious accident involving a car and a pedestrian on the northbound carriageway of the A40, near the services at Raglan on Sunday.
Gwent Police are appealing for witnesses after the pedestrian was taken to hospital with serious injuries.
A 69-year-old woman has died in a car crash on the A449 in Monmouthshire.
Officers from the fire and ambulance service attended and dealt with the collision yesterday afternoon, which involved one vehicle.
The road between Raglan and Usk was closed southbound to allow emergency services to attend the scene - buy has now re-opened.
Another person was treated for minor injuries at the Royal Gwent Hospital in Newport.
Anyone who saw the crash is asked to ring Gwent Police on 101 quoting log 419 27/12/13.
The A40 is closed because of a jackknifed lorry between the A449 (Raglan) and the A4042 / A465 Heads Of The Valleys Road (Abergavenny).DIVERSION:via the B4598