Police closed the M61 close to junction 8 (Chorley North Link Interchange) at around 5.15pm today (June 1).
Officers say this due to a "concern for safety incident."
It is not yet known when the motorway will reopen, but police are urging motorists to avoid the area.
A spokesperson for Lancashire Police said: "The M61 is currently closed close to Junction 8 while we deal with a concern for safety incident.
"We would ask all motorists to avoid the area if possible and to find alternative routes."
Heavy delays are expected as a result of the closure and diversions have been set up in the area.
A spokesperson for Highways said: "The M61 southbound J9 (Brindle M65) to J8 (Chorley A674 A6) is currently closed due to a police incident.
"There is also a minor diversion on the northbound at J8 as traffic is having to exit the motorway, to rejoin via the entry slip road."
Further details about the diversions can be found by clicking HERE.More to follow...