The A47 is shut this morning between Thorney and Guyhirn after a road collision.
The road is closed in both directions and is likely to remain so for a long time.
Motorists are urged to avoid the area.
An air ambulance has also been called.
Cambridgeshire police said: “Due to a serious RTC (Road Traffic Collision) the A47 between Guyhirn and Thorney Toll is closed and is likely to be closed for some time. The air ambulance has been called. Please avoid the area.”