Operation Stack has been activated in Kent in response to a build-up of lorries heading to France caused by industrial action in Calais.
Freight traffic is being held on the coastbound carriageway of the M20 between Junctions 8 and 9.
The “emergency measure” is designed to prevent gridlock on Kent’s road network.
Ferries between Dover and Calais are suspended due to a 24-hour strike by staff at the French port, which began at 8am on Thursday.
Ferry operators DFDS and P&O Ferries normally run a total of up to 50 sailings per day on the route.
DFDS has switched one of its Calais ships to the Dover-Dunkirk route to provide extra capacity.
Freight vehicles and passengers due to travel between Dover and Calais with DFDS on Thursday were shipped onto Dover-Dunkirk sailings instead.
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 in order to resume normal operations as soon as possible.
“Please note that there may be delays to services when the Port of Calais reopens.
“We apologise for any delays or inconvenience as a result of the industrial action in France.”
Dover and Deal MP Natalie Elphicke said: “Last week Dover went into gridlock when there were delays putting its traffic management systems in place quickly.
“I am pleased to see that lessons were learned from last week and that Operation Stack was stepped up today quickly in response to French industrial action.
“These traffic management systems are vital to keep Dover clear so that local residents can get out and about to work, to go to school, shops and access healthcare.
“If lorries and port traffic follow the rules and stick to the traffic plans when there is disruption – whether from security alerts, French strikes or leaving the EU – their cross-channel journey will be all the smoother and quicker, and they will be playing their part to keep Dover clear for residents.”
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