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The A20 coastbound carriageway at Dover was closed for almost 14 hours after three lorries collided close to the Samphire Hoe entrance.
Police received the call on Wednesday at 3.45pm and fire and ambulance services attended the scene where almost 10,000 gallons of oil was spilt.
One man is in a critical position and suffered multiple injuries to his lower body.
Police spokesman Rosy Alexander confirmed the serious crash investigation team was looking into the smash.
"The road was opened again at 5.30am," she said.