Eurotunnel services have been suspended after a "massive invasion" of more than 100 migrants at the French terminal.
A "large and co-ordinated" group broke through fences and stormed the Channel Tunnel at around 12.30am, Eurotunnel said.
A spokesman said: "It's a massive invasion and intrusion by a very large and co-ordinated group of migrants.
"They are being gathered up by the police authorities."
He added: "It's clearly an organised attack when it comes in such a large number, there are over 100 in this one group.
"They arrived together an in a well-organised manner, broke through the fences and all clearly knew where they were going."
Services have been suspended but there are no trains stopped in the tunnel and passengers have been directed to use the ferry to carry on with their journey.