Schoolchildren have been forced to wait for 16 hours at the Port of Dover with supplies of food and water running low.
One mother said her 13-year-old son had been in the same position since 7.30pm on Saturday and was ‘starving’, having only been offered a KitKat at midnight.
Gillian Charlton, 43, said that her son’s group, who are due to go skiing in Italy, had no access to free running water and were only allowed to get off their coach to use a Portaloo.
“It’s shambolic,” she told The Sun.
“I don’t think they have access to running water and can’t get off - only to use the Portaloo.
“They were given a KitKat at midnight.
“Children are feeling unsafe. They are all starving.”
Extra ferries were run overnight on Saturday to help try and clear the backlog but customers were still facing long queues on Sunday.
A spokesman for the port said: “P&O have some coaches waiting at the cruise terminal and DFDS have some at service stations in Kent.
“Once coaches are processed in an operator’s lane, more are being sent to the port. Currently, the estimated total time is six to eight hours dwell time.”
P&O Ferries apologised to customers on Sunday, saying some will face waits of four to five hours.
It is thought a higher-than-expected number of coaches as well as slow border processing is to blame for the delays.
More than 300 coaches departed from Dover on Saturday.
Coaches take longer to process than cars because each person has to go through border checks individually.
Officials said ferry companies had received 15 per cent more coach bookings over the Easter holidays than expected, the BBC reported.
The port previously declared a critical incident and said the delays were “due to lengthy French border processes and sheer volume”.
Meanwhile, Home Secretary Suella Braverman has rejected suggestions that Brexit could be the cause of delays.
Ms Braverman told Sophy Ridge On Sunday on Sky News that it would not be fair to view the delays as “an adverse effect of Brexit”.
She said: “What I would say is at acute times when there is a lot of pressure crossing the Channel, whether that’s on the tunnel or ferries, then I think that there’s always going to be a back-up and I just urge everybody to be a bit patient while the ferry companies work their way through the backlog.”
She also downplayed any fears that delays at Dover could become a regular occurrence that risks ruining school holiday plans.
She suggested that in general “things have been operating very smoothly at the border”.
Speaking on the BBC’s Sunday With Laura Kuenssberg programme, she added: “I don’t think this is the state of affairs to go forward.
“I think we have got a particular combination of factors that have occurred at this point in time.
“This will ease. I ask everybody to check their journey times carefully, but it is a busy time of year.”
On Saturday, passenger Rosie Pearson described the travel scenes in Dover as “carnage” as she was stuck for 16 hours with her husband and two teenagers.
Ms Pearson, 50, is an environmental campaigner from Essex and was travelling to Val d’Isere in the French Alps on an overnight bus.
Shadow levelling up secretary Lisa Nandy said “a range of factors” have caused the delays, but she claimed the Government had not planned for what was going to happen post-Brexit.
She told Sophy Ridge On Sunday that ministers had “known for a very long time that they needed to make sure that there were resources in place to deal with additional paperwork checks”.
She added: “The point is not whether we left the European Union or not. The point was that we left with a Government that made big promises and once again didn’t deliver.
“I really feel for the families that are trying to get away for a Easter break, people who have been caught up in this chaos, people whose livelihoods are threatened.
“It didn’t need to be this way.
“If the Government got a grip, got down to brass tacks and started doing their actual job, all these things could be avoided.”