A migrant died on Tuesday trying to reach Britain through the Channel Tunnel, a French official in the Pas-de-Calais region said.
One of the six sections of the tunnel was closed for investigation, with traffic severely disrupted. It was as yet unclear how the migrant died.
"Following the discovery of migrants on a freight shuttle, early this morning, the shuttle was immediately stopped," said the official.
"During an investigation by border police, a deceased migrant was found in the tunnel," the official added.
Earlier Eurostar reported that services were delayed because of "trespassers in the tunnel".
UPDATE: Restricted tunnel access as a result of trespassers within tunnel mean current morning Eurostar services will be delayed.— Eurostar (@Eurostar) July 7, 2015
UPDATE: Sections of the tunnel are closed at present due to trespassers on a Eurotunnel shuttle. Apologies - delays will affect our services— Eurostar (@Eurostar) July 7, 2015
Eurotunnel which runs passengers and freight trains from Calais to the UK also had to suspend services due to migrants in the tunnel and was advising some passengers to re-book their journeys.
Confirmation that due to migrants found on freight shuttle, we expect delays to Passenger service of 3hrs from UK & 60mins from France. ^LE— Eurotunnel LeShuttle (@LeShuttle) July 7, 2015
We recommend that due to the length of delays, day trip customers travelling today rearrange their travel to an alternative date. ^LD— Eurotunnel LeShuttle (@LeShuttle) July 7, 2015
The firm has been calling on French authorities to do more to secure the area around the Channel Tunnel terminal in Calais.
A spokesman told The Local that migrants, around 3,000 of whom are amassed in the Calais area, try to break into the terminal on a daily basis.
"We are finding migrants in the terminal and we are asking police to round them up. We are not a police force we are transport service," he said.
"We are asking French authorities to reinforce their protection of the terminal given the current circumstances ofthe strike and the ongoing migrants crisis."
The migrant crisis was exacerbated last week when striking French ferry workers blocked access to the tunnel causing Channel services to be halted and provoking huge tailbacks on roads leading to Calais.
Migrants took advantage of the chaos to jump aboard stationary trucks.
Tim Waggott, the port's chief executive, released an open letter saying four days of strikes in Calais had cost the British economy around €1 billion pounds (€1.4 billion , $1.5 billion).
"How could you equate the importance of keeping such valuable trade moving with the incredible disruption caused at a major international gateway -- Calais -- by the mob rule of a small number of aggrieved militant Frenchmen? We certainly cannot," Waggott wrote.
Last week Britain and France agreed to increase checks and hand over more resources to try to dissuade migrants from trying to get to the UK.
Home Secretary Theresa May met her French counterpart Bernard Cazeneuve in Paris to discuss the issue which has created friction across the Channel.
"Taking into account the worsening migration crisis in the Mediterranean and the repercussions on Calais, where 3,000 migrants are currently based, the two ministers decided to reinforce their cooperation," a joint statement issued after the meeting said.
Moreover, joint information campaigns aimed at explaining to migrants the realities of the British asylum and welfare system, so as to dissuade flows of migrants to the Calais region, will be pursued and stepped up."
No precise figures were given, with the French ministry saying that was still under discussion.