Kent Police were called at 6.45am to a two-vehicle collision on the clockwise carriageway of the M26.
Two vans were involved in the collision, one ending up on the grass bank, the other in lane 2 of the two lane carriageway.
The M26 clockwise between M20 at J3 and M25 at J5 was closed while the vehicles were recovered and was fully reopened just after 11am. Lane 1 was briefly reopened around the scene of the incident to allow some of the traffic to pass.
The M26 was closed in both directions while the air ambulance landed and took off.
A man from Medway was cut free from his vehicle and taken to Kings College Hospital in London with what were believed to be serious but non-life threatening injuries. The man is believed to be in a stable condition.
Three other people were taken to a local hospital with what were believed to be minor injuries.
Kent Fire and Rescue Service and South East Coast Ambulance Service attended.