A P&O ferry with nearly 400 passengers has returned to Dover after being prevented from entering the port of Calais by protesting French fishermen.
The vessel had sailed from the Kent port before industrial action affecting cross-channel ferry services began.
P&O Ferries, SeaFrance, Norfolkline and LD Lines have all been affected.
The blockade at the French ports of Calais, Boulogne and Dunkirk has also led to the implementation of Operation Stack on the coastbound M20 in Kent.
Hundreds of lorries are being held between junctions eight and nine of the motorway to keep the port town clear.
Non-freight traffic is being diverted onto the A20.
Eurotunnel is continuing to take freight and people who have already secured bookings. Eurostar services are unaffected.
Kent Police has advised hauliers, lorry drivers and motorists to consider whether their journeys are absolutely necessary and where possible to avoid travelling over the next 48 hours.
The action by the French fishermen is against EU fishing quotas set by the Common Fisheries Policy.
It is not known when the blockade will be lifted.