The collision near Newton-le-Willows happened around 6.45am and forced Highways officers to stop all traffic between southbound junctions 23 (Newton-le-Willows) and 22 (Warrington (North) A49).
Traffic has now been released but long delays remain on the approach, with heavy congestion as far back as junction 27 (Standish, Parbold).
According to Highways England, there are currently delays of approximately one hour over an 11-mile stretch of carriageway.
Motorists are being urged to allow extra time for their journeys or seek an alternative route route.
Normal traffic conditions are expected to resume between 8.50am and 9.25am.
The delays and congestion is likely to affect journeys to Wigan, Ashton-in-Makerfield, Skelmersdale, St Helens, Newton-le-Willows and Warrington (A49).
The Emergency services attended the scene but it is not known whether anyone has been seriously injured in the collision.
Matrix signs are informing drivers of 40mph speed limits on the approach from junction 24 (St Helens, Ashton A58).