The A1 has been shut at Wansford after a collision involving a number of vehicles.
There are long queues on the road as a result of the collision, which involved two lorries and a car.
Earlier the road was shut in both directions - but now the southbound carriageway has re-opened. There are still long delays in the area though.
One man has been airlifted to Addenbrooke’s Hospital with serious injuries.
Sgt Craig Wheeler from the BCH Road Policing Unit said: “We were called to a three vehicle collision on the A1 northbound at Wansford around 11am. It involved one car and two HGVs.
“The driver of one of the HGVs has sustained serious injuries and been taken to Addenbrooke’s Hospital by air ambulance. All other occupants are uninjured.
“The road should be fully open by 2pm to allow for recovery.
“Witnesses to the collision, or anyone with dash cam, are asked to contact us on 101.”
A spokesman for Cambridgeshire police said: “We were called at 10.14am today to reports of a road traffic collision on the A1 at Wansford.
“The collision involved two lorries and a car. Officers are at the scene, together with paramedics and firefighters. The air ambulance has also been called to the scene.
“As a result, the northbound carriageway of the A1 is currently closed and motorists are urged to avoid the area.”
Traffic is being diverted onto the A47 at Wansford.