A traffic backlog in Kent caused when industrial action in France halted ferry sailings from Dover is likely to take until the early hours to clear.
More than 1,000 lorries were parked on the M20 in Operation Stack
The Port of Calais confirmed to Dover Harbour Board on Wednesday lunchtime that the port was returning to normal.
But Kent Police said drivers should continue to avoid the M20 coastbound between junctions eight and 12 where 1,000 lorries had to be parked.
The M20 was closed when Operation Stack was put in place on Tuesday afternoon.
Miles of traffic built up on the motorway, with some drivers being forced to spend Tuesday night in their vehicles.
Police provided food, water and toilet facilities for those stranded.
Insp Roy Kingston said some lorry drivers had been able to leave Dover via a limited service to Dunkirk.
"But a large number have got freight booked through the Calais port... and they're not going anywhere.
"It is a situation that is outside of our control," he said.
Keith Southey, of Dover Harbour Board, said the situation had been made worse because of the increased amount of freight traffic leading up to Christmas.
Other motorists using the M20 coast-bound were being diverted at junction eight onto the A20 through Lenham.
Police have been providing food and water for those stranded
However, some told the BBC that they saw foreign lorry drivers trying to beat the traffic queues on the M20 by following the diversions, snarling up the smaller roads.
The port of Calais was blockaded by members of the Calais Chamber of Commerce, who were striking over the dismissal of a cleaner.
"It is an absolutely crazy situation," said Brian Rees, spokesman for ferry operator P&O.
"We are a £1m-a-day business and we have lost virtually a day's business.
"But look what it has done around the county - even one of the hospitals was on earlier saying they can't get people to appointments."
The Freight Transport Association said there had been at least 20 strikes and blockades in Calais over the past 10 years.
It estimated the cost of the current disruption at £2m.
Kent MEP Richard Ashworth said: "This huge and costly inconvenience has been going on for far too long and it's just not acceptable.
"I have asked the European Commission for assistance in finding a solution because our free passage into and out of the EU is being severely hampered."