The eastbound carriageway is fully closed at Junction 25 near Brighouse following a breakdown and a spillage on the carriageway.
Traffic officers and West Yorkshire Police are at the scene.
The incident is causing 30 minute delays on journeys towards Leeds, with four miles of queuing traffic spanning back to Junction 24.
Average speeds are less than 10mph.
Drivers are advised to avoid the area where possible and First Bus has warned that its services may be delayed.
Metro Travel has warned that congestion is building across West Yorkshire bus networks.