THE M40 is currently closed between junction nine for Bicester and junction 10 for the Cherwell Valley Services because of an overturned lorry.
The vehicle is blocking the whole northbound carriageway and one lane of the southbound carriageway is also shut.
A Highways Agency spokesman said the incident between a lorry and a car at 5.45pm had resulted in one serious injury.
Drivers are being diverted off the M40 and onto the A34, being advised to follow the solid circle symbol on road signs.
Oxfordshire Fire and Rescue is also in attendance but said they did not need to release any casualties from the vehicles.