Migrants have rushed the Channel Tunnel at Calais repeatedly for a second night and one man was crushed by a truck in the chaos.
The incident came as Eurotunnel said it had blocked more than 37,000 such attempts by migrants to reach Britain since January.
There were conflicting reports of the numbers of people involved in the chaos, ranging from 150 to as many as 1,200. But it was agreed there had been about 2,000 attempts on each of two successive nights.
Many British officials have expressed growing alarm at what they see as a potential influx of foreigners, although it is not clear how many people have successfully made the passage.
A group of about 25 migrants was seen getting off a public bus in Calais on Wednesday with a police officer who left them by the side of the road. Several said they were returning from a night of trying to get across the Channel.
Natacha Bouchart, mayor of Calais, said about 150 to 250 migrants tried repeatedly overnight to reach the Eurotunnel. French officials said it was the second night of mass attempts on the tunnel.
Gilles Debove, a police union official, counted about 2,000 attempts for a second night running. Mr Debove said officers pushing back the migrants counted between 750 and 1,200 people.
Ms Bouchart told France Info radio that migrants are trying to reach England from France "at all costs" - first crossing a busy motorway and then trying to stow away on trucks waiting to board trains. She says Britain, France and the Eurotunnel need to work together on the issue.
The man killed overnight, believed to be a Sudanese migrant in his mid-20s, was crushed by a truck as he tried to stow away, Mr Debove told The Associated Press.
Attempts among the thousands of migrants camped in Calais to reach England have intensified with labour strife involving Eurotunnel, which has seen striking ferry workers repeatedly disrupt the railway to protest job cuts.
British Prime Minister David Cameron, speaking during his visit to Singapore, described the crisis as "very concerning" but said that there was no point in "pointing fingers of blame".
The British government has agreed to an extra £7 million of funding for measures to improve security at Calais.