The Port of Dover has declared a “critical incident” due to long queues leading to a ferry terminal.
It has also accused France of “woefully inadequate” border control staffing which is ruining the summer getaway for thousands of families.
Holidaymakers booked on sailings from the Kent port reported being stuck in five-hour queues to complete border checks before they can check in for their ferry.
The port said in a statement it has made “significant investment” to increase its capacity, and shared traffic volume forecasts “in granular detail with the French authorities”.
It went on: “Regrettably, the PAF (police aux frontieres) resource has been insufficient and has fallen far short of what is required to ensure a smooth first weekend of the peak summer getaway period.”
Delays at Dover are causing tourist and freight traffic to be stuck on gridlocked roads in the area.
One Twitter user wrote: “I’m booked onto 8am ferry from Dover and it’s total gridlock. Moved 50 metres per hour.
“At this rate it’ll be 34 hours before I get to the port!
“I have a screaming toddler and three-month-old.”
Another described how they have been “waiting five hours and still not in the port”.
The person added: “Sat in lanes waiting to get to border control. Zero movement.”
Ferry operator P&O Ferries told passengers: “There are currently queues in excess of four hours to reach the border controls.
“Our check-in remains free flowing and once you reach us, we will put you on the first available sailing.
“Please arrive prepared for a prolonged wait. Carry snacks and additional water with you.”