Traffic is stopped both ways on the M1 between Northampton and Milton Keynes on Friday morning after a lorry caught fire.
HIghways England reported the blaze between junction 14 and junction 15 northbound just before 10am.
A spokesman confirmed: "Traffic has been stopped on the northbound carriageway due to the fire but the southbound will also need to be stopped temporarily due to thick smoke.
"Please be aware there are long delays on approach to this incident and average journey times are now 60 minutes above normal for this time of day, with 4½ miles of congestion.
"Please allow extra time for your journey and use alternative routes where possible."