Tense arguments over queue jumping erupted and passengers started directing traffic themselves amid an apparent absence of staff to control the flows of cars during one of the busiest days of the year.
One passenger, Elizabeth Goodfellow, said that 16 lanes of traffic were being channelled into seven French border control posts, causing substantial delays.
Crossings between Calais and Dover have been complicated ever since Britain left the European Union in 2022.
Port officials on both sides say that stepped-up border controls planned for 2023 risk adding to the time each vehicle spends at checkpoints.
In July, tens of thousands of passengers travelling from Dover to France faced massive delays amid British claims of insufficient French staff on hand to check passports of departing travellers.