Police closed the motorway in both directions between junctions 10 and 9 shortly after 4am due to an "ongoing incident".
It has now been confirmed that officers had been responding to a "concern for safety report" that involved a man on a bridge above the carriageway.
Lancashire Police said the man had fallen from the bridge onto the motorway, and has suffered serious injuries to his arms and legs.
Ambulance crews were called to the scene and the man has been taken to the major trauma centre at Royal Preston Hospital for emergency treatment.
A spokesman for North West Ambulance Service said: "We received a call to the scene at 4.09am and sent an ambulance and response vehicle.
"A man was taken to hospital with major trauma related injuries."
Motorists were asked to avoid the motorway whilst emergency services worked at the scene, with a diversion route put in place along the A679 Accrington Road.
The motorway has since reopened in both directions and any traffic delays have now cleared.
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