Highways England has tweeted the closure saying the crash happened between Junctions 9 – 10, Oxford to Cherwell Valley Services.
The post was timed at 2.13pm so delays are likely to continue for some time to come.
They say: “The #M40 is currently closed northbound between J9-J10 due to a multi-vehicle collision. Emergency services are at the scene, however please allow extra time for your journey and plan ahead. Please follow @HighwaysEAST for further information.”