Kent Police was called to the scene at 8.16pm on Wednesday 5 January 2022 following a report of a collision involving an ambulance and a cement lorry.
Four people were injured in the incident, two of them were seriously hurt and the air ambulance was in attendance.
Officers from the Serious Collision Investigation Unit have commenced and investigation and are asking anyone with dashcam footage prior to the incident to come forward. Anyone who witnessed the collision is also being asked to contact officers.
It is anticipated that the A21 will be closed for the foreseeable future and motorists are being asked to check the route before travelling.
If anyone has any information that may assist with the investigation please call 01622 798538 quoting RY/CS/03/22. You can also email firstname.lastname@example.org