Long traffic jams were created outside the Port of Dover, Britain's main gateway to Europe, on Saturday, and officials warned that the disruption could be worse than the one seen on Friday.
Due to slow border checks, as well as the regular flow of goods lorries, people who started their trips at the start of the British school summer break had to wait for a long time, reports Reuters.
The Kent Resilience Forum, which brings together local councils and emergency services, declared a "major incident", while Port of Dover CEO Doug Bannister said travellers could face delays of up to six hours on Saturday.
The UK government has blamed the problems on a lack of French border force staff, while France says more checks are needed because Britain is no longer a member of the European Union.
Dover and the French port of Calais have "juxtaposed" border controls in which French authorities check passports on British soil before departure, and vice versa in France.
"We were expecting that today was going to be a busier day than yesterday," Bannister told BBC radio. "Yesterday we processed about eight and a half thousand cars going out, today we were predicted to be around 10,000, so it is going to be a very busy day down here."
Bannister said the number of French border staff at Dover had increased following Friday's disruption.
French regional prefect Georges-François Leclerc said that at midday, out of the 9,000 to 10,000 vehicles scheduled to pass on Saturday, 60% had passed without any issue.
British Foreign Secretary Liz Truss, who is competing to succeed Boris Johnson as prime minister, insisted on Saturday that the French were to blame.
"This is a situation that has been caused by a lack of resource at the border. That is what the French authorities need to address and that is what I'm being very clear with them about," she told reporters in Kent, southeast England, after meeting party members.
Travelers heading for the Eurotunnel service at Folkstone were also facing delays. Queues stretched two miles (3.2 km) back from the entrance.
The port delays came as some airports also struggled to recruit enough staff to manage a post-pandemic rebound in travel, leading to chaotic scenes at London airports in recent weeks. Railway travel has also been periodically disrupted this summer by labour strikes.
"800km of traffic":
At the start of the busy summer travel season, people in other European countries told of similar travel problems.
On Saturday, traffic in France was particularly heavy around Paris and between Lyon and Valence.
Authorities recorded a peak of 790 kilometers (490 miles) of traffic jams on major roads used by tourists Saturday lunchtime, reports The Euronews.
This peak was less than the 930 kilometers (577 miles) recorded in France a year ago.
As the peak of the tourist season in Croatia draws near, there is more traffic on all roads that lead to tourist spots along the Adriatic coast.
According to Jelena Ivuli, a coordinator for the Croatian national sea shipping company Jadrolinija, passengers have been arriving in waves since the early hours of Saturday morning, with large crowds forming at ferry port entrances.
Over the weekend, they anticipate over 75,0000 passengers and over 15,0000 vehicles.
In Switzerland, holiday traffic at the Gotthard north portal was backed up for 15 kilometers, with wait times of up to two and a half hours.