Thousands of Eurostar travellers faced “nightmare” queues at Gare du Nord in Paris after a border control IT failure meant passengers could not board trains.
It comes as the UK is braced for travel disruption on road, rail and sea on Monday as millions return from their Easter getaways.
One passenger, Charlie Daffern, 36, from Cheltenham, said all trains had been delayed for at least an hour at the Eurostar terminal in Pairs.
“It’s a nightmare here. We have been stood in the queue for check-in/security for over an hour and a half. Probably another hour to go”, he said.
“People are becoming very restless and some people panicking as they have flights to catch from Heathrow this afternoon. I take it all with a pinch of salt. The main problem is lack of communication.”
Loic Kreseski, 25, who lives in east London, said “hundreds and hundreds” were in queues at the station.
“I heard French border officers saying that they had never seen that. People are upset due to the delays and the fact that you have to stand still for hours. It’s very upsetting when we know the price of the tickets.
“I would say that easily more than a thousand people are queuing in Gare du Nord. (I am) frustrated especially when we know the price of the tickets, the lack of announcements and customer service.”
Travellers using the Eurotunnel Le Shuttle service have also reported “chaos”, with long traffic queues.
About 3.96 million drivers are expected to make their journeys in Britain on Easter Monday, causing delays on many major routes.
It comes after rail and air passengers endured long queues while some Dover-Calais ferries remained suspended at the weekend.
Planned engineering works on the UK rail network are also likely to mean more delays for travellers.
Network Rail has been carrying out 530 engineering projects costing a total of £83 million, which have meant the closure of the West Coast Main Line between London Euston and Milton Keynes for four days since Good Friday due to upgrades to the existing line and HS2 work.
Parts of the railway between Birmingham and Coventry have also been closed, along with lines around Crewe station.
Passengers at Manchester, Heathrow and Gatwick airports have also contended with long queues.
Lucie Spencer, 25, a salon owner from Lancashire, said customers were dealing with “frustrating” and “annoying” delays after her flight was held for over an hour because of apparent staff shortages.
She said: “Queues were very long, we were in Terminal 2. They moved consistently but slowly. The mood of the airport was generally calm but you could hear people moaning, of course, as it’s not fun standing in queues for so long.
“It’s definitely due to major staff shortage, TUI had basically no check-in desks open, just self check-in, which seemed to cause the huge queue. Security was then huge queues as there was only three of eight security lanes open.
“Queues to get in all bars and restaurants, meaning we had to give up to it so as to not miss our flight.
“Still sat on plane, should have taken off at 8.30am but the luggage wasn’t loaded on to the plane in time.”
A representative of travel group TUI said: “We can confirm that unfortunately due to staff shortages at Manchester Airport today, some customers are experiencing longer-than-usual queue times at check-in. Please be assured that our teams are working as quickly as they can.
“We have contacted all customers due to depart in the next two weeks with advice on travelling with potential wait times in airports and have more information available on our website.”
Manchester Airport has been approached for comment.
The suspension of Dover-Calais sailings has led to a shortage of capacity on the key route and contributed to large queues of lorries on the roads approaching the Port of Dover in recent days.
To add further worry, supplies of petrol and diesel at filling stations in some areas of the country have been running at around half their usual level.