Trouble flared in Calais as lorry drivers came under attack from migrants in an "unprecedented" and "organised" disturbance, British officials said.
Truckers forced to slow on motorways near the cross-Channel port had their lorries attacked, with locks broken and roofs slashed as migrants tried to climb inside, witnesses said.
One said that French police used tear gas to try to disperse the crowds but appeared to be "overwhelmed" by the large numbers of migrants.
Another described the crowds as looking like something from "the aftermath of a football match", with many migrants carrying white flags or banners.
Trouble broke out on what was one of the busiest days of the year for cross-Channel freight traffic, a spokesman for Channel Tunnel operator Eurotunnel said.
Chris Yarsley, of the Freight Transport Association (FTA), witnessed the scenes and said he was "flabbergasted" by the trouble, which was described as "unprecedented".
He said: "They were attacking vehicles, breaking the locks of trucks, slashing roofs of the lorries and climbing in the back of them.
"French police were highly visible and were taking extreme measures to break up the crowds, including using tear gas and closing the motorway in order to control the situation, but appeared to be overwhelmed by the numbers."
Mr Yarsley said the migrants appeared to have organised the attacks by creating disturbances in the nearby town centre to act as a diversion.
On the Les Calaisiens en Colere Facebook page, a local described a group of migrants "running around with iron bars, stones and hammer".
Eurotunnel spokesman John Keefe said Chunnel services were not disrupted but there was clearly an organised approach to the disturbances.
He said: "It was clearly well organised and orchestrated. And it came on one of the busiest days of the year for freight, with 6,000 to 7,000 trucks around today.
"Opportunity-wise they would have known that and clearly information is out there. The security at the tunnel and the additional police meant they didn't get to the tunnel.
"It turned out to be a neutral day from our perspective but clearly there was a level of orchestrating behind the events we saw."
The trouble is the latest in a regular series to break out in Calais where some 6,000 people who have fled war, poverty and persecution are camped at "The Jungle".
On Wednesday truckers were again targeted after being forced to slow down by migrants walking in the middle of the motorway.
Three were spotted climbing on to one lorry's roof before eventually being coaxed down by a French police officer wielding a baton.
British freight chiefs believe such trouble impacts heavily on the £89 billion worth of UK trade which passes through Calais annually.
There have been repeated demands for the French and British authorities to secure the safe passage of freight, particularly after repeated trouble during the summer.
The Road Haulage Association (RHA) has said that despite the deployment at Calais of around 1,300 security officials, including CRS riot police and French gendarmerie, it is still not enough to protect drivers.
RHA chief executive Richard Burnett said many truckers now refused to stop within 150 miles of Calais to avoid the "absolute mayhem" caused by some migrants intent on getting to the UK.