The northbound and southbound carriageways are struggling to cope with congestion between junctions 27 (Leyland) and 31 (Tickle Trout, Preston).
The worst of the 11-mile queue of traffic is a 3.5 mile tailback between Leyland and Bamber Bridge, where traffic is at a standstill.
Heavy traffic on the M6 is also merging with congestion from the M61 and M65 around Bamber Bridge Interchange (junction 28).
Highways England said there are no reports of break-downs or traffic collisions.
The agency said the high volume of traffic is "likely due to summer getaways', with families heading north to the Lake District for the weekend.
A Highways spokesman said: "We have had no reports of incidents, so congestion is likely due to the sheer volume of traffic with the summer getaway season."
Traffic England said the congestion is expected to last until at least 3.45pm