French border control booths have been "seriously understaffed" leading to huge queues in Dover, the port said.
A Port of Dover spokesman said in a statement: "French border control booths have been seriously understaffed overnight with only three booths available for tourists out of a potential seven.
"At one stage, only one French officer was available to check passengers on hundreds of coaches, resulting in each coach taking 40 minutes to process."
It added that it "shares the frustration" of drivers and said it had raised concerns with the government over "manning levels" and the government had raised it with the French government.
France is to ramp up its military efforts against so-called Islamic State in Iraq following the Bastille Day lorry attack in Nice.
President Francois Hollande announced that France would supply heavy weapons to Iraqi forces as early as next month.
But President Hollande said there are no plans to deploy troops on the ground there or in Syria.
Eighty four people died after Mohamed Lahouaiej Bouhlel drove a lorry into crowds on the Promenade des Anglais on July 14.
Five alleged accomplices have been charged with terror offences.
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Police who have been searching through Nice lorry attacker Mohamed Lahouiaej Bouhlel's background say they discovered he had only recently been radicalised.
In the run-up to the attack he had been searching the internet for material about radical Islamist movements.
ITV News Security Editor Rohit Kachroo reports from Nice:
The people of France have vented their anger at a government they accuse of failing to protect them against terrorism.
The country's prime minister was booed as he attended a memorial service for the victims of the Nice attack, with shouts of "murderer" and calls for him to resign.
Eighty-four people have died following Thursday's attack, the third major atrocity in France in just 18 months.
ITV News correspondent Emma Murphy reports:
The Nice attacker took selfies on the promenade hours before mowing down 84 people with a lorry on Bastille Day, prosecutors have revealed.
Paris prosecutor Francois Molins said that on the day of the attack, Mohamed Lahouaiej Bouhlel appeared to have spent much of the day on the Promenade des Anglais, taking selfies on the beach and the walkway.
It was also revealed that around eight months ago he took a picture of a news story headlined "Man deliberately rams car into cafe terrace", seemingly the first sign he was planning something.
Around the same time, Bouhlel showed a friend a video of a hostage being decapitated.
The Nice lorry attacker did several scouting missions on the Promenade des Anglais before carrying out the deadly Bastille Day attack, prosecutors have revealed.
Mohamed Lahouiaej Bouhlel had been searching online for July 14 celebrations, seemingly planning his attack, which left 84 people dead.
The prosecutor said there was no proof the attacker had direct links to the so-called Islamic State group, but internet searches showed he was interested in radical Islamist movements.
Bouhlel paid €1,600 (£1,330) on July 4 to hire the truck used in the attack and in the days before the massacre he was caught twice on CCTV rehearsing the journey that he would take on July 14, prosecutors said.