Traffic officers are carrying out the road block between southbound junctions 8 (Chorley) and 6 (Bolton North, Horwich).
Maintenance workers have been tasked with making urgent repairs to a large pothole in the carriageway.
The road block will allow traffic to keep moving, but at a reduced speed of 20mph.
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Matrix signs have been activated on the motorway advising drivers to approach with caution.
The rolling road block is expected to last until around 9.15am.