Police have been called to the scene, which is on the southbound carriageway between J15 for Northampton and 14 for Milton Keynes
Two lanes - lanes two and three - are reportedly blocked by a pair of lorries.
The AA traffic news website says: "Vehicles are passing the scene with care through lane one.
"However there are also multiple cars involved stranded... partially blocking lane one."
Highways England has advised people to avoid the area if possible. An official diversion is in place.