National Highways - formerly known as Highways England - said congestion is causing tailbacks from junctions 29 (M65, Lostock Hall) to 31A (B6242 Bluebell Way, Longridge).
The agency said traffic has struggled to recover after an accident earlier this morning between J31A and J32.
The accident scene was cleared by 10.50am, but as of 1.30pm there is still slow-moving traffic northbound from junction 29 to 31A.
There is also reports of congestion on the M61, with delays from Chorley to the motorway interchange with the M65 at Walton Summit.
National Highways say the approximate travel time through congestion is around 20 minutes.
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