The A142 has been closed at Chatteris following a serious collision between a car and a lorry.
The incident happened at 2.40pm at Mepal and the road has been shut off by police between Chatteris and Sutton.
The air ambulance is on the scene, along with emergency services. At least one person is believed to have serious injuries.
Drivers are advised to avoid the area if possible as the collision has caused severe tailbacks.