Migrants are fighting each other to get on lorries stuck in traffic jams caused by a Calais port workers strike, an organisation representing transport firms has said.
Tyres and hay bales were being burned on the A16, adding to the problems, according to the Freight Transport Association (FTA).
Donald Armour, the FTA's international manager, said: "We have heard that the strikers have set up a blockade on the A16 with burning tyres and hay bales, bringing the main motorway to a halt.
"It costs about £50 an hour to have a lorry stuck in traffic. If you're a company with half a dozen lorries, it adds up to a lot of money being lost.
"It's their worst nightmare and not a good day to be travelling."
With the worsening migrant situation in Calais, Mr Armour said the FTA was "really, really worried" about someone getting seriously hurt.
"There is a lot of fighting between the migrants who all want to be on the best part of the road to get on to the lorries," he said.
"We haven't had a fatality but it's not good. The situtation is definitely worse than it has ever been."
Truckers were being advised not to stop within about 60 miles (97km) of Calais, to stick with other drivers and make sure padlocks are always kept on their vehicles.
Meanwhile, a partial blockade of the Channel Tunnel terminal in Coquelles has been removed and Eurotunnel is working to clear the backlog of traffic.
Kent Police said that while the Port of Calais remained closed, services from Dover to Dunkirk were unaffected and extra crossings were being arranged.