DOVER, England (AP) — Trucks inched slowly past checkpoints at the English port of Dover and headed across the Channel on Thursday to the French port of Calais, after France partially reopened its borders with Britain following a scare over a rapidly spreading new coronavirus variant.

Only a small fraction of the thousands of frustrated truck drivers and travelers have so far made it through the mass gridlock at Dover on Christmas Eve, held up by slow delivery of the coronavirus tests now demanded by France. One by one, trucks passed toward ferries and trains that link Britain with France, as authorities checked that drivers had the negative virus tests required to cross.

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 logistical issues that have prevented freight getting to the port, we have unfortunately only been able to transport 144 trucks out of Dover,” shipping company DFDS said. The company is scrambling to arrange Christmas Day sailings to help resolve the problem, it added.

Officials warned the backlog could take days to clear. One U.K. road haulage expert estimated there could be 8,000 to 10,000 trucks caught up in the chaos near Dover but a government minister said it involved some 4,000 trucks.

French Ambassador Catherine Colonna said two dozen French firefighters have been sent to Dover, bringing 10,000 coronavirus tests for drivers desperate to get home for Christmas. British Transport Secretary Grant Shapps said British and French authorities have agreed to keep the border between the countries open throughout Christmas to help truck drivers and travelers get home.

Dozens of countries around the world began barring people from Britain last weekend after Prime Minister Boris Johnson said large areas of southern England including London had to be placed under harsher restrictions to curb a new, more contagious version of the virus.

France’s temporary shutdown of the border raised the most concerns, since France is a major conduit for trade and travel between Britain and the continent. The U.K. relies heavily on cross-Channel commercial links to the continent for food at this time of year, especially fresh fruit and vegetables.

The announcement of the coronavirus variant came as Europe has been walloped by soaring new virus infections and deaths. Europe as a whole has recorded over 500,000 virus-related deaths, according to a tally by Johns Hopkins University that experts agree is probably an undercount due to missed cases and other factors.

Britain has seen soaring infection rates in recent weeks, with many hospitals nearing their capacities. On Wednesday, the country reported another 744 deaths and a record 39,237 confirmed new cases. Christmas gatherings and festive shopping were cancelled for millions at the last minute in a bid to control the spread of the virus.

London now has the highest rate of people testing positive in the country, according to the latest figures published by the Office for National Statistics. It estimated that 2.1% of people in the capital had COVID-19 in mid-December, compared to around 1.18%, or one in 85 people, for the wider population in England.

The majority of new positive cases in London were believed to be the coronavirus variant, the statistics office said.

In France, officials defended the country's handling of the border after the EU’s transport commissioner issued unusually strong criticism.

Commissioner Adina Valean, of Romania, tweeted: “I deplore that France went against our recommendations and brought us back to the situation we were in in March when the supply chains were interrupted.”

France’s European affairs minister, Clement Beaune, tweeted back that France had “exactly followed the EU recommendation” and is now “more open than other European countries” to arrivals from Britain.

China on Thursday became the latest nation to suspend flights to and from the U.K.

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Angela Charlton contributed from Paris.

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