Travellers heading to the UK have suffered delays of up to six hours as they queued at the Port of Calais, reports BBC News.
Ferry operators DFDS and P&O Ferries apologised for the long wait times at UK border controls on Saturday.
P&O added extra vessels were used for passengers who missed their sailing, as queues continued into the evening.
Speaking to BBC News, passenger Josh Williams said he was stuck waiting in Calais for five hours on Saturday to get a ferry back to the UK.
He shared pictures of long lines of cars filled with families trying to get back to Dover ahead of the new school year starting for many in England next week.
Earlier in the afternoon, DFDS warned on social media the queues could potentially last for six hours for people travelling from Calais.
The firm said: "Due to high levels of traffic at the Port of Calais, there are currently waiting times of up to six hours to complete all controls."
However, it added traffic at the ports in Dunkirk, in France, and Dover, in the UK, were "free-flowing through check-in and border controls" throughout the day.
P&O Ferries said on Twitter: "We sincerely apologise for the wait times at the port of Calais today.
"Checked in vehicles have been unable to reach the loading lanes due to queues at border control. This is then causing vehicles to be backed up past the check in booths."
A later post from the company added: "We have put on an additional sailing this evening from Calais to help with the passengers that have been stuck at border control.