Eurotunnel said that train services had been suspended in both directions Tuesday after protesting French sailors got onto the tracks of the line that links France and Britain and torched tyres.
"We have been notified that protesters have gained access to rail tracks which means that for safety reasons Eurotunnel have to temporarily suspend their service," the firm said in a statement.
A spokeswoman told AFP that protesters had "got onto the tracks and were burning tyres".
Earlier Tuesday, sailors from the French company MyFerryLink blocked the entrance to the tunnel that connects Britain and France as part of their protest against plans to sell two of its three boats to a competitor.
The protesters also backed up traffic for kilometres by sitting down on the A16 motorway.
Some of the migrants living in camps near the port, who use Calais as a jumping off point to reach Britain, took advantage of the halted traffic by trying to climb aboard vehicles.