Emergency services were called to the scene on the northbound carriageway between junctions 32 (Broughton) and 33 (Hampson Green) at approximately 11am on Monday (August 1).
National Highways warned there were delays of up to an hour on approach, with approximately five miles of congestion as crews tackled the car fire.
Two out of three lanes reopened past the scene at around 12.35pm as the burnt-out car was recovered.
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All lanes reopened at approximately 12.50pm but seven miles of congestion and slow moving traffic remained in the area.
A spokesman for National Highways added: “Please allow extra journey time this afternoon.”
Lancashire Police closed the road in both directions as emergency services attended and urged motorists to avoid the area where possible.
A spokesman for the force said: “We were alerted to a report of a collision between two cars on the A6 at Garstang, near to the Bellflower pub, at approximately 11.27am today.
“The collision partly blocked the road, causing slow traffic in the area, and there was then a second collision involving two cars nearby.
“No one was injured in the collisions but the A6 was blocked while the vehicles involved were removed.”
Officers confirmed the road reopened at around 1.25pm.