The incident is London-bound, between junction 8 for Hollingbourne and junction 9 for Ashford, resulting in both carriageways being closed.
Five fire engines and a bulk water carrier attended, and crews wearing breathing apparatus put the fire out using compressed air foam and a hose reel jet.
There were no reported injuries and the cause is not yet known. The affected section of the M20 is set to remain closed for a number of hours while debris is cleared and the scene is made safe.
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