The M6 south of Carlisle will be closed for several hours on Tuesday while emergency repairs take place.
The work, under the pedestrian bridge at Southwaite services, was scheduled to close two lanes, with one lane open to traffic.
However, a 'defect' was discovered by Highways England which means the whole of the northbound carriageway must now close between junction 41 at Catterlen Interchange and junction 42 at Carlisle South.
A diversion is in place, using the parallel A6 east of the motorway between the two junctions.
The closure was put in place at 12.30pm and could remain in place until 8pm this evening.
Highways England is advising drivers making essential journeys during the lockdown to plan journeys carefully and allow extra time if they need to use the M6 and diversion route this afternoon.