The incident took place on Monday (August 26) at around 11.30am on the northbound carriageway between junctions eight for Chorley and nine for the Walton Summit Roundabout.
Lane three of three is closed, as per Highways England.
No details of the crash are yet known.
The motorway isn't expected to clear until 2.30pm with normal traffic conditions expected by 3pm.
There are currently delays of 20 minutes against expected traffic.
The incident means that there are delays where the M61 joins the M6, with delays of 10 minutes against expected traffic.
An AA spokesman said there is an average speed 15 mph for traffic joining the M6.