The collision has happened northbound between J9 at the Clayton Brook interchange and J30 where the M61 joins the M6.
The northbound carriageway has been closed between those junctions with traffic being diverted along the M65.
Emergency services are dealing with the incident, which happened shortly after 9am. Highways England announced that the crash is involving a motorcyclist but no details on other vehicles or injuries have been released.
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A spokesman for Highways England said: "Lancashire Police and Highways England traffic officers remain on scene. Collision investigation work will be undertaken.
"Road users are advised to exit the M61 at J9 on to the M65 westbound. Travel to J1, exit and join the M6 northbound to continue their journey.
"There is approximately two miles of congestion on approach to the closure at J9. Please plan ahead of your journey and allow extra time. "