Officers are dealing with a two vehicle collision which occurred on the Northbound carriageway at Lymm.
The collision involved a car and a flatbed lorry which were both travelling in the same direction.
The driver of the car has been airlifted to hospital. The Southbound carriageway was closed to facilitate the helicopter and is now open.
Officers remain working at the scene to establish the cause of the collision. The Northbound carriageway will remain closed until at least 6pm to facilitate this work.
Traffic is being diverted from junction 19 at Tabley Westwards along the A556 where it re-joins the motorway at junction 20.