A car fire blocked the M25 anticlockwise in the middle of the afternoon rush hour.
Traffic began to tail back from the incident at junction two with the A2 (Darenth Interchange) to junction three with the M20/A20 (Swanley Interchange).
By 5pm two lanes were open, but one remains closed, causing long delays in the area.
Two fire engines were called to the blaze which was put out by 4.40pm.
No one is thought to have been injured.
A police spokesman said: "Officers were called at 4.08pm to a report that a car was on fire on the anti-clockwise carriageway of the M25 at junction two.
"Lane one around the scene of the fire was closed."