Motorists spend night in their cars amid 15 hour queues on roads to Dover
Motorists face more misery on the roads to Dover as queues continue amid disruption expected to last until Monday.
Some people were forced to spend the night in their cars after getting stuck in jams leading to the port.
UK Border Force officials have been drafted in to work with French border police after the Government admitted motorists had suffered "extraordinary disruption".
On Sunday morning Kent Police said people could expect delays of 10 hours on the A20, with around 12 miles of queuing traffic back to junction 11 of the M20.
Queues have eased slightly, authorities at the port said, but are likely to continue as more people set out to try and make the crossing to France.
Kent Police said the disruption is down to a "vast volume of holiday traffic" coupled with delays caused by heightened security at the border in the wake of terror attacks.
Increased checks were put in place by French authorities at the port in light of recent terror attacks, but questions have been raised about staffing levels to deal with the huge number of people travelling at this time.
After complaints that just one French officer was available to check in coaches on Friday night into Saturday, port authorities said six booths - four for cars, one for coaches and one for freight traffic - were manned overnight into Sunday.
The Home Office said UK Border Force officials are in place to help but added they cannot say how many as they do not go into "operational details".
The Government said Kent police will also be "proactively managing" traffic to get drivers through more quickly.
A Government spokeswoman said: "We recognise the security pressures that French law enforcement organisations are under at Dover and we have agreed the UK Border Force will assist the PAF (French border police) with border checks to remove the backlog.
"We understand that there has been extraordinary disruption in the Dover area today but safety is paramount.
"Measures are also being taken on the approach to the port where Kent Police will be proactively managing traffic to speed up the process."
People travelling, many heading off for a summer break, spent up to 15 hours at a standstill in queued traffic while water supplies were dropped along the jam by police helicopter on Saturday.
A Sikh humanitarian relief organisation also pitched in with the effort, delivering nearly 6,000 bottles of water along with snacks to the stranded motorists.
Conservative MP for Dover Charlie Elphicke, who was stuck in traffic for around two hours on Friday evening, said there had been a lack of forward planning which led to "poor transport management" and urged the Government to apologise for the "traffic nightmare".
Shadow home secretary Andy Burnham accused the Government of being "caught ill-prepared once again", warning the Prime Minister should have expected heightened security checks in France.
Among those affected by the disruption was multiple sclerosis sufferer Tanya Cudworth whose journey to Dover from Tunbridge Wells took 20 hours.
The 50-year-old, who was travelling to a Frankfurt clinic to undergo stem cell treatment for her condition after raising £5,000 for the trip, described the experience as "absolutely horrendous".
P&O Ferries said passengers will be booked on the first available sailing when they arrive at check-in.
Eurotunnel said there is a waiting time of around an hour to check in at the Folkestone terminal and a further 30 minutes on the terminal.
Those setting off on journeys on Sunday have been advised to bring food and water supplies.