A further 800 military personnel have been sent to Kent to help thousands of lorry drivers waiting to cross into France on Christmas Day.
Some 1,100 troops have been deployed as part of the operation at the English Channel border after French Covid-19 restrictions caused severe disruption at the Port of Dover.
Thousands of hauliers are now spending Christmas Day in their cabs despite efforts to clear the backlog of lorries.
Army personnel will be testing drivers for coronavirus and distributing food and water, the Ministry of Defence (MoD) said.
Transport Secretary Grant Shapps said on Friday that more than 10,000 tests had been carried out, of which 24 came back positive for the virus.
France closed its border last Sunday following the discovery of a fast-spreading mutant Covid-19 strain in the UK.
Drivers must now show proof of a negative coronavirus test result taken within the past 72 hours before crossing into the country.
About 4,000 vehicles, including 2,000 freight lorries and 1,000 cars, have been cleared for departure at Dover since the border reopened on Wednesday, a port spokesman said.
However, about 5,000 lorries remain unable to get home yet, despite some progress in testing drivers in their vehicles at nearby Manston Airport, on a closed section of the M20, and in the town of Dover itself.
Some have already spent nearly a week stranded due to the diplomatic impasse.
Traffic was moving smoothly through Dover on Friday morning, with French firefighters drafted in to help test drivers.
The Polish military’s Territorial Defence Force arrived later in the day to help with testing and food distribution, the country’s UK embassy said on Twitter.
They have codenamed their operation “Zumbach”, after the famous Polish Second World War pilot Jan Zumbach, who fought for the allies in the Battle of Britain, the embassy said.
Germany’s ambassador to the UK, Andreas Michaelis, said some German hauliers had managed to make it home for Christmas, while others remained in Kent.
He tweeted: “Some of the German lorry drivers we’ve been in touch with are on their way home or at home already. Others sadly remain stuck.
“I sincerely hope things will start moving for them soon. This is a difficult Christmas. Our thoughts are with them.”
Southeastern railway and Network Rail arranged for food to be delivered to drivers stuck in Operation Brock on the M20.
Seven trains carrying crates of food for the hauliers have left London in the past 48 hours, with the Salvation Army distributing the items.
HM Coastguard said its teams in the Dover area had so far delivered 3,000 hot meals, 600 pizzas, 2,985 packed lunches and 17 pallets of water to those waiting.
The MoD said additional soldiers were deployed on Friday as part of Operation Rose to support the 300 personnel already there.
“We are deploying a further 800 personnel to Kent today to support an increase in the testing capabilities to help clear the backlog of vehicles and ensure traffic can begin to move at a closer to normal pace through Dover,” the MoD tweeted.
Mr Shapps said he had instructed the army to take control of testing and HGV management operations in Kent in order to get “foreign hauliers home with their families as quickly as we can”.
He tweeted: “A huge thank you for the tireless efforts of our troops, police, civilian testers, council planners & port & ferry workers for giving up their Xmas to get people home.”
The Government said catering vans would provide hot food and drinks to hauliers stranded at Manston, with Kent County Council and volunteer groups providing refreshments to those stuck on the M20.
There are more than 250 toilets at Manston, with a further 32 portable toilets added to existing facilities on the M20.
A Port of Dover spokesman said ferry services ran throughout Christmas Eve night and will continue on Christmas Day to help ease congestion.
Traffic was moving more quickly at the Eurotunnel on Thursday, with around 2,000 lorries expected to depart during the day.