Trucks inched slowly past checkpoints in Dover, UK, and headed across the Channel to Calais on Thursday, as France conditionally reopened its UK border.
Freight from Britain along with passengers who can provide a negative COVID-19 test are now free to reach French shores after France relaxed its two-day blockade sparked by a scare over a new coronavirus variant.
Officials however warned the backlog could take days to clear, as the number of lorries has increased to six thousand, at least.
Days of delay and frustration have already led to frayed tempers and clashes with police.
COVID-19 tests are being conducted by military personnel. Results usually come within half an hour.
On the French side, the vast Calais port - which normally takes in up to 4,000 trucks a day - remained quieter than usual due to the testing challenges in Britain.
Watch more on the story from Dover in the above player.