Holidaymakers are stuck in long queues heading into the Port of Dover - with French immigration being blamed for causing a "critical incident".
Delays are "in excess of four hours", P&O Ferries said, adding: "Please arrive prepared for a prolonged wait. Carry snacks and additional water with you."
It added that anyone travelling today should "allow at least six hours to clear all security checks".
One traveller said they were moving "50 metres per hour", tweeting: "At this rate it'll be 34 hours before I get to the port!"
Another said: "Sat in lanes waiting to get to border control. Zero movement."
The port said "woefully inadequate" French staffing was to blame for "major disruption" and a "critical incident" had been declared....
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