Ferry operator P&O has cancelled all Dover to Calais crossings due to a blockade by French fishing boats.
The blockade at the port of Calais is also causing motorway disruption in Kent, police have said.
Fishing fleets have been stopping ships entering or leaving Calais, Boulogne and Dunkirk since Tuesday, in a dispute over fishing quotas.
The French general workers' union CFDT has threatened to blockade Eurotunnel and Eurostar on Thursday.
P&O has said the protest was costing £1m a day and it was preparing a compensation case against the fishermen.
The ferry operator has not said in which jurisdiction such a compensation case might be heard.
Services to Boulogne and Dunkirk have also been called off until further notice, P&O said.
Norfolkline passenger Charles Suckling, who was stranded at Dunkirk overnight, said the French Red Cross had been handing out thermal blankets to passengers who were in their cars, and also setting up camp beds and sleeping tents in the ferry terminal building.
At six o'clock, eight fishing boats went back into the port of Calais and the whole thing kicked off again
The French army had also arrived to deliver food rations, he added.
Richard Barclay, who was due to sail from Calais to Dover on P&O with his family on Tuesday night, was making his journey back to Maidstone by train on Wednesday morning.
They spent the night with relatives in Bruges and managed to rebook their journey.
But he said he and his family arrived at the ferry port on Tuesday to see about 30 or 40 coaches all carrying children, who were stranded and waiting to cross the Channel.
"There were coach-loads of children, either schools or football teams," he said.
The blockades have led to Operation Stack being implemented in Kent
"It's the children I feel sorry for. They were probably at the end of their Easter break and had run out of money.
"They were spilling out into the car parks, playing football, and generally hanging out as teenagers do."
P&O spokesman Chris Laming said blockades were lifted temporarily overnight, allowing the ferry operator to repatriate 3,000 passengers who were waiting on the quayside.
He said: "We got them all home by about two o'clock this morning, but at six o'clock, eight fishing boats went back into the port of Calais and the whole thing kicked off again."
Mr Laming said fishing vessels had strung themselves across the entrance to the port, and the blockades operated "on the principle that we dare not run them over".
Kent Police said part of the M20 was closed again on Wednesday to cope with the disruption.
The force said Operation Stack - in which lorries awaiting Channel crossings park on the coastbound M20 - was lifted overnight but then brought back in.
Police advised cross-Channel passengers to contact travel operators for further details.
The Freight Transport Association (FTA) has renewed calls for an overnight lorry park in Kent.
FTA policy manager for the South East, Natalie Chapman, said: "Operation Stack costs industry hundreds of thousands of pounds every time it is employed."
She added: "This current situation adds a sense to urgency to our continued calls for an overnight lorry park in Kent with enough capacity for the thousands of lorry drivers that depend on this gateway to and from the Continent."
French fishing unions have said they are protesting at ever tougher EU-imposed quotas, and demanding the French government take a stand on their behalf or offer more financial assistance.
On Wednesday, French ministers refused protesters' demands for increased cod quotas, but said they might offer extra financial support.
Agriculture minister Michel Barnier said he would meet industry representatives to discuss further support for fishing boats in difficulty, but the government offered no suggestion the quota limits would change.
Government spokesman Luc Chatel said France obtained a 30% increase in cod quotas in the Channel, in the latest annual negotiations.
The EU has said that limiting the size of fishing catches is the best way to stop stocks being wiped out through over-fishing.
Two MEPs for the South East have called on the French government to put an end to the dispute.
British fishermen have as much right as French fishermen to complain
Richard Ashworth MEP
Labour MEP Peter Skinner said: "I am furious that yet again French fishermen have been allowed by the authorities in France to blockade ports essential for UK trade and tourism".
He said the action was hurting the British economy and stretching police services.
Richard Ashworth, Conservative MEP, said: "British fishermen have as much right as French fishermen to complain about the failings of the EU's Common Fisheries Policy (CFP).
"We do need to overhaul the CFP and the Common Agricultural Policy but it is the French government that often acts as a roadblock to reform."
And he added: "It is time the French government put an end to this. Our transport links should never operate at the mercy of French fishermen."
Information from P&O said that neither P&O Ferries nor the three other ferry companies operating out of Dover were sailing to Calais on Wednesday, nor were there any services to Boulogne or Dunkirk until further notice.
Long-term travellers were advised to make their way to the port and make alternative arrangements, which could include rail travel.
Day trippers were advised to rebook their journeys.
Fishing fleets are blockading ports in a dispute over fishing quotas
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