Some 2000 migrants tried to get into the Channel Tunnel terminal in Calais in an attempt to reach the UK, operator Eurotunnel says.
The company has described the scale of the incident overnight on Monday as unprecedented.
Services through the tunnel were severely disrupted as a result. Passengers were held up for about an hour on the British side and 30 minutes on the French side on Tuesday.
Such disruption has become common as thousands of migrants, mostly from Africa and the Middle East, have set up camp around the northern French port and regularly try to board trucks travelling by the rail tunnel or by ferry to Britain.
An official count at the beginning of July found that about 3000 migrants were camping in Calais and trying to get across the Channel.
Eight migrants have died this summer trying to reach Britain through the Channel Tunnel.
There were delays to services last week when the body of a suspected migrant was found on the roof of a Eurotunnel train at the terminal in Folkestone, southern England.
In the latest incident, a spokesman for Eurotunnel said the migrants were trying to enter the site "between midnight and 6am", adding: "It was the biggest incursion effort in the past month and a half.
"All our security personnel, that is nearly 200 people, as well as police were called in."
Another Eurotunnel spokesman said a number of people were injured and there was damage to fences as people tried to board shuttles.
"It is an almost nightly occurrence," the spokesman said. "We're trying to run a travel business here."
Meanwhile, the UK has agreed to provide an extra £7m towards efforts to step up security at the Channel Tunnel railhead in Calais.
- BBC / AFP / Reuters