Video report by ITV News Correspondent Juliet Bremner
Lorry drivers and police have clashed in Kent as drivers stuck at the border have been warned it could take days to clear the backlog.
Others honked their horns and shouted "we want to go home" in protest at being stuck at the border, despite the border with France reopening after a mass Covid testing agreement was reached between the two sides.
More than 6,000 HGVs are being held in the county, with drivers being tested for Covid-19 before they are allowed into France.
Kent Council leader Roger Gough said the first 20 trucks have now entered the Eurotunnel to make the crossing.
One man has been arrested following disturbances in both Dover and at nearby Manston Airport which is currently being used to park thousands of stranded lorries.
Police said he is being held for obstructing a road.
ITV News Correspondent Juliet Bremner reports from Dover
A police car was also damaged during a disturbance at Manston, Kent Police said.
Many more vehicles are stuck at the port and along the M20 after France closed its border to the UK on Sunday night in a bid to halt the spread of the new, more infectious Covid strain.
Drivers, eager to get home for Christmas, have been warned it could take days to clear the backlog and those not already at the border are being urged to keep away.
Footage from the port of Dovers shows a handful of police officers attempting to push back a small crowd.
Rail, air and sea services between the UK and France reopened on Wednesday morning, with residents and citizens of France allowed to return home if they return a negative Covid test.
The testing of lorry drivers began late on Wednesday morning and the Ministry of Defence said 170 personnel would be helping NHS Test and Trace to carry out the task.
Transport Secretary Grant Shapps said there continued to be “severe delays” despite testing now taking place.
He tweeted: “Testing has begun as we look to get traffic moving again between the UK and France.
“However, French border police only acting on agreement from this morning and severe delays continue. Please AVOID Kent while the backlog is cleared. Arriving in the area will delay your journey.”
While Communities Secretary Robert Jenrick told ITV News it could take a "few days" for things to return to normal, with many hauliers eager to get home for Christmas.
'Please stay where you are, don't come down to Kent' - Robert Jenrick urges drivers
Drivers will receive rapid lateral flow tests - which can give results in about 30 minutes - followed by a PCR test if they come back positive.
Those who return a second positive result will be offered "Covid-secure" hotel accommodation.
Shadow health secretary Jonathan Ashworth branded the situation in Dover "chaotic".
"It's been extraordinarily chaotic hasn't it," he told ITV News.
"What an end to the chaotic year this has been for Boris Johnson."
Under the agreement announced between the two countries, admittance into France will only be granted to those travelling for urgent reasons – including hauliers – French citizens, and British citizens with French residency.
One of those caught up in the traffic jams surrounding the area was Germany's ambassador to the UK, Andreas Michaelis, who said he was scheduled to meet with German truck drivers at Manston Airport in Ramsgate on Wednesday, however was not able to reach the airfield due to a two-day blockade.
Writing on Twitter, he said: “Went to Manston Airport today. Scheduled to meet up with German truck drivers. Last stretch difficult. Could not reach the airfield. Could only speak to them on the phone.
“Still very difficult situation for them. Too little information.”
Mr Shapps has also announced a temporary relaxation of drivers’ hours for hauliers - increasing the driving limit of nine hours to 11 - to help them get across the border.
The terms of the deal raises questions about what it means for other EU-national lorry drivers who are in the UK.
While Britons will not be allowed to cross over the border as part of the deal.
There has been disagreement about the number of lorries stuck in the area, with the government accused of underestimating the figures.
The Road Haulage Association (RHA) estimates between 8,000 and 10,000 delayed lorries are now in Kent and its surrounding areas - in lorry stops and at depots waiting for borders to reopen and to cross the Channel.
There may be shortages of fresh goods until the backlog of lorries is cleared, the British Retail Consortium has warned.
Andrew Opie, the group’s director of food and sustainability, said: "It is essential that lorries get moving across the border as quickly as possible.
"Until the backlog is cleared and supply chains return to normal, we anticipate issues with the availability of some fresh goods."