Operation Stack has been implemented on the M20 to help prevent gridlock following delays at the Port of Dover due to industrial action in Calais.
Ferries between Dover and Calais were suspended earlier because of the strike by staff at the French port.
The 24-hour closure of the Port of Calais began at 08:00 BST. Ferry operators are switching some routes to deliver passengers to Dunkirk instead.
Freight vehicles are being transferred to the next available Dunkirk sailing.
DOVER-CALAIS | Industrial action by French Unions has commenced in Calais from 0800 today for 24hrs. Services have been suspended. Booked Calais? Proceed to Dunkirk to be transferred on to the next departure. Travelling from Dover? Proceed to port to be transferred to Dunkirk.— DFDS UK Updates (@DFDSUKUpdates) September 24, 2020
Operation Stack is an emergency measure designed to prevent gridlock in Kent. Kent Police work with Highways England and the county council to put it in place.
It was activated on the M20 earlier to allow lorries to line up to enter the port.
Under the measure, freight is separated into two queues on either side of the coast-bound carriageway between Junctions 8 and 9.
One lane is used for traffic heading to the Eurotunnel terminal and one lane is for port traffic. The middle lanes are kept clear for emergency vehicles.
Non-freight traffic is diverted off the motorway and onto the A20.
It is the second time this month it has been used, the first was following a request by Counter Terrorism Policing to increase security checks at all UK ports for an "ongoing operational activity".
The Port of Dover said in a statement: "We will continue to monitor the situation closely in liaison with our ferry partners and the Port of Calais.
"Please note that there may be delays to services when the Port of Calais reopens and services resume to normal."