Police were called at 3.40pm to reports of a collision between a man and a lorry outside the Esso on North Road.
The victim, a man in his 30s, has been taken to hospital by emergency services with serious leg injuries.
Officers also arrested a 39-year-old man from South Ockendon on suspicious of driving under the influence at the scene.
The service station will remain closed for the rest of the night.
Both lanes have now been reopened.
Tags: Thurrock, South Ockendon