UK border control staff will help with French security checks to reduce the huge delays at Dover.
French authorities have increased controls at the border in the wake of terror threats, and combined with a larger number of people taking a summer break, it has resulted in hours of delays for motorists in the area.
There were hold ups of up to 15 hours on Saturday while many drivers and passengers were forced to spend the night in their cars on the A20 and M20 as well as other surrounding roads toward the ferry port and delays are expected to continue on Sunday.
Travellers were warned that they still face delays of several hours if travelling to Dover and border force staff in the UK have been drafted in to help with the additional security checks to try and get things moving.
"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," a government spokesperson told the BBC.
The additional checks were "understandable", said Conservative Party chairman and former transport secretary Patrick McLoughlin, speaking on the BBC's Andrew Marr show. But, it was "unacceptable the way people have been left in the lurch".
"There have been discussions between our government and the French government to try and ease the situation as much as we possibly can," he added.
The changes at border control are also affecting Channel Tunnel journeys, with an additional waiting time of 60 minutes.
"It's one of the busiest travel periods of the year for our service and due to recent events in France security checks are heavily reinforced," Eurotunnel said in an update to passengers.
"We have made extensive plans for these days and are working closely with the Border Authorities however these checks are having an impact on the flow through our check-in and on our terminal."