A nine-lane-wide queue stretched alongside the white cliffs throughout Saturday morning on the approach to the border where French guards were checking passports.
Thousands of rail workers are also striking, meaning only around half the number of trains will run in certain areas, while other places may have none at all.
Port of Dover officials said overnight that over 35,000 people had passed through on their way to France on Friday and had told travellers on Saturday not to arrive more than three hours before their sail time.
At 7am, they wrote: “The current average processing time through to the border is 120 minutes, as per our peak travel plan for the busiest times.
“Rest assured, you will be on the next available sailing upon reaching check in.”
Members of the RMT are on strike
/ PA ArchiveIn addition, rail strikes mean disruption on major lines in and out of London, including Avanti West Coast, London Northwestern Railway, Northern, Southeastern, Southern, South Western Railway, and Thameslink.
Other affected services include c2c, Caledonian Sleeper, Chiltern Railways, CrossCountry, East Midlands Railway, Gatwick Express, Great Northern, Great Western Railway, Greater Anglia, Heathrow Express, LNER, TransPennine Express and West Midlands Railway.
There are also delays or part closures on the Bakerloo, District, Hammersmith and City, Piccadilly, DLR, and Overground.
A Rail Delivery Group spokesperson said the strikes were disrupting the plans of families during the summer holidays.
They said: “This will lead to disappointment, frustration and financial strain for tens of thousands of people. We apologise for the inconvenience caused and understand the impact on individuals and businesses.
“Our advice is to check before you travel.”
The ongoing industrial dispute has been worsened by plans to close most ticket offices.
In a message to families whose summer holiday plans have been affected by the latest walk-out, the RMT senior assistant general secretary said “we need to stand together rather than fight each other”.
Standing on a picket line outside Euston Station, Eddie Dempsey said: “What I’d say to them is, if they’re honest, people are going to find it difficult on a strike day.
“But everyone in this country is finding it hard when it’s not a strike day.
“And the reason for that is because we’ve got a Government that is presiding over a massive cost-of-living crisis, everybody’s wages have been falling, all of our public services are under-funded, we can see all of the services we rely on in the country in a state of managed decline, nothing’s getting better.”
