One man has been found dead as migrants made about 1500 attempts to enter the Eurotunnel terminal in a desperate bid to get to England, a situation the British prime minister warned was "very concerning".
Authorities in London were planning emergency talks on Wednesday (local time) over the migrant crisis, which has now claimed nine lives since June and sparked major travel disruption in a peak European holiday season.
"Our team found a corpse this morning and the firefighters have confirmed the death of this person," said a Eurotunnel spokesman on Wednesday.
The migrant, a man of Sudanese origin believed to be aged between 25 and 30, was hit by a truck that was leaving a cross-Channel ferry, the police source said.
The overnight attempts at storming the Eurotunnel terminal came after about 2000 bids to enter the site were recorded the night before, in what was described as the "biggest incursion effort in the past month and a half".
For several weeks, there have been many attempts by migrants to enter the Eurotunnel premises, with the number of people trying growing significantly in recent days.
"Everything happened overnight, and at 6:00am, the police still had quite a lot of work to do," said the police source of the latest attempts, adding that "between 500 and 1000 migrants" were still around the tunnel site.
Security at the Calais port was stepped up in mid-June, driving migrants who previously tried to stow away on trucks that take ferries across the Channel to try their luck smuggling through the undersea tunnel.
Authorities are finding it difficult to police the whole terminal area, which stretches over 650 hectares and has 28 kilometres of fencing.
According to the last official count in early July, around 3000 migrants, mainly from Ethiopia, Eritrea, Sudan and Afghanistan, were camped out in Calais, waiting for the right moment to try to make a dash for Britain.
Long queues of lorries were already beginning to form at the entrance of the tunnel very early on Wednesday morning.
Speaking in Singapore, British Prime Minister David Cameron announced that Home Secretary Theresa May would chair a meeting of the government's Cobra emergency committee to discuss the issue.
"This is very concerning," he told reporters. "We are working very closely" with French authorities to address the situation.
"I have every sympathy with holidaymakers" trying to get to the continent from Britain or people heading the other way, said Cameron.
The issue has been a thorn in the side of Franco-British relations for years and May met her counterpart, French Interior Minister Bernard Cazeneuve, for talks on the crisis on Tuesday.
May announced that London would pay out an additional £7 million to help France secure the Eurotunnel site on its side of the Channel.
Eurotunnel said on Wednesday it had blocked more than 37,000 migrants trying to enter its French premises and make their way to Britain since January and spent €13 million on boosting security.
"The pressure we are now under every night exceeds that which an operator can reasonably handle, and calls for an appropriate reaction from the states" of France and Britain, Eurotunnel said in a statement.