Traffic is seriously congested on the motorway near Chorley following a car crash that left one person with major injuries.
The M61 southbound was blocked between junctions 8 and 9, near Chorley, due to a traffic collision involving four people at around 1.08pm.
It is believed a car had crashed with a central reservation.
One person was seriously hurt and unconscious, and was taken by road ambulance to Royal Preston Hospital. Two others suffered minor injuries and are also expected to be hospitalised. The fourth person was unharmed.
Traffic is now at a standstill at points along the motorway, with delays reaching as far as the M55 and also on the M65 and M6. The road is expected to be cleared between 6pm and 6.15pm, with traffic conditions returning to normal between approximately 7pm and 7.15pm.
Emergency services, including an air ambulance, attended the scene. Fire crews from Preston, Bamber Bridge and Greater Manchester were called at 1.10pm and assisted paramedics in providing first aid to the wounded.
A spokesman for Highways England said: "Please allow extra time for your journey and seek an alternative route."