Protesting French sailors halted Eurostar trains by again blocking the entry to the Channel Tunnel in Calais on Tuesday, AFP reporters said, with migrants using the opportunity to try to break into stationary vehicles.
Eurostar warned of disruption to its high-speed train services between France and Britain.
Local authorities said there had been attempts by some of the thousands of migrants camped out around the port in Calais to break into lorries, in a repeat of dramatic scenes captured on camera last week.
The migrants, whose presence has long caused friction between London and Paris, go to dramatic lengths to smuggle themselves into Britain, and have even been recorded trying to swim across the Channel.
"We have registered break-in attempts by migrants this morning at the Eurotunnel site," said a spokesman for the local council.
The tunnel is used for drivers travelling between Britain and France, whose cars are transported on special trains, as well as for Eurostar passenger train services.
The French ferry company workers are protesting plans by Eurotunnel to sell two of their cross-channel ferries to rival Danish firm DFDS.
Eurotunnel announced in May it was halting its operational partnership with MyFerryLink due to legal complications, and this month decided to sell its ferries to DFDS.
The Danish ferry operator has said it plans to provide work for only 202 of the current 600 MyFerryLink workers.
The sale of the two ferries would leave MyFerryLink with just one boat in operation, meaning over half the workforce faces redundancy.