Some 2,000 migrants tried to enter the Channel Tunnel terminal in Calais on Monday night in an attempt to reach the UK, operator Eurotunnel has said.
A number of people were injured, a spokesman for Eurotunnel said, without elaborating.
Eurotunnel is facing a daily struggle with migrants who attempt to smuggle themselves into Britain, sometimes with fatal consequences.
The latest incident caused serious delays to Eurotunnel train services.
Passengers were held up for about an hour on the British side and 30 minutes on the French side on Tuesday, French news agency AFP reported.
Meanwhile, the UK has agreed to provide an extra £7m ($10.9m) towards efforts to step up security at the Channel Tunnel railhead in Calais, Home Secretary Theresa May has announced.
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: "There was some damage to our fences - which we'll have to repair - as they tried to board shuttles. Fortunately, there wasn't any damage to shuttles. Unfortunately, a number of people were injured.
"It is an almost nightly occurrence - we're trying to run a travel business here."
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.
AFP says an official count at the beginning of July found that about 3,000 migrants - mainly from Ethiopia, Eritrea, Sudan and Afghanistan - were camping in Calais and trying to get across the Channel.
French Interior Minister Bernard Cazeneuve held talks in London on Tuesday with the UK home secretary on the migrant issue.
Speaking after their meeting, Ms May said: "The French and UK governments are working in close collaboration and co-operation on this issue which affects us both.
"We are both clear that we need to ensure we are dealing with the terrible criminal gangs, the people smugglers, who are making a profit out of the human misery of many people."
Eurotunnel is seeking compensation from the British and French governments for disruption caused by illegal migrants.