The two incidents affected the same stretch of northbound carriageway, between junction 27 (Parbold, Standish) and junction 29 (Bamber Bridge).
Delays caused by the rush hour collisions, which occurred within 30 minutes of each other, caused delays between 7.50am and 9am.
Both incidents have been cleared but Highways are warning of residual queues between junctions 27 and 31 (Preston).
The first accident, near Charnock Richard Services, happened in the outside lane (lane three) around 7.50am.
According to an eyewitness, the collision involved a white BMW, a grey Volkswagen Passat and a large white van.
Traffic was held between junctions 27 (Standish) and 28 (Leyland) as traffic officers worked to clear the scene.
The stricken vehicles were moved to the hard shoulder to await recovery whilst emergency services attended the scene.
But delays resumed shortly after the carriageway was cleared due to a second incident between junction 28 (Leyland) and junction 29 (Bamber Bridge).
It is understood that this accident involved a grey Vauxhall Corsa and a grey 4X4 near Bamber Bridge.
The two crashes caused long delays with an 11-mile tailback of traffic from Bamber Bridge to Standish.
The situation was made worse by rush hour traffic joining the M6 from the M6 at junction 30.
The crashes also created congestion as far back as junction 26 (Orrell Interchange) in Wigan, which serves commuters to Skelmersdale, Liverpool, Southport and the M58.
It is not yet known whether anyone has been injured in the collision
Highways are currently indicating delays of approximately 30 minutes as congestion slowly eases.