Two lanes of the carriageway on the M1 southbound are closed just before Junction 15.
The problem is due to a vehicle fire, say officials from National Highways East.
"There are long delays of at least 30 minutes above usual journey times approaching J14. Please take care on the approach," said a spokesman.
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M1 closed southbound at Milton Keynes following serious collision involving van and crane
Bucks Fire and Rescue Service is at the scene.