The Manor Road and Reynolds Lane bridge runs over the motorway. Local reports say that the closure is due to a piece of material falling from the bridge and hitting a car.
The police have closed the southbound carriageway at junctions 17 and 18, with the northbound remaining open at present. The closure was announced in police tweets at about 6am. No estimate has been given for when it will reopen, but the police reported at about 8.30am that a bridge inspector was on the scene.