A man, believed to be a migrant, has been electrocuted after trying to jump on board a Eurostar train due to travel from Paris to London.
It is understood he vaulted between two trains in an attempt to get into the protected zone for departures, but touched a live overhead wire.
A police official at Gare du Nord station says he's in a "very serious condition".
It comes after one man died after 1,500 migrants tried to make their way to the Eurotunnel platforms overnight - among 37,000 who have been stopped since January.
The Sudanese man, aged in his late 20s, was crushed by a truck and is believed to be the ninth migrant killed at the tunnel since the beginning of June.
On Monday night, about 2,000 migrants tried to break through the terminal's security fence – and it was reported that two people were hit by a train, although there were no reports of fatalities.
Eurotunnel spokesman John Keefe said none of the 1,500 who tried to break through the fences to the tunnel's platform on Tuesday night were successful, adding that the crisis affects freight services - not passenger services - and the migrants are not getting "anywhere near" the tunnel itself.
A spokesman for Groupe Eurotunnel, which runs the Channel Tunnel, said: "The continuous pressure exerted every night is above and beyond that which a concessionaire can reasonably handle and requires a constructive and appropriate response from both governments."
Prime Minister David Cameron has described the migrant crisis in Calais as "very concerning" - and stressed the UK government will do "everything it can" to improve the situation.
At a news conference in Singapore, Mr Cameron said he had "every sympathy" for holidaymakers who have had their travel plans disrupted but he advised against "trying to point fingers of blame".
Security
Britain has agreed to spend an extra £7m (€9.95m) on improving security at the Channel Tunnel railhead in Coquelles and 1.2 miles of fencing from the recent NATO summit in Newport will secure each side of the platform at Coquelles and will be installed by the end of the month.
The latest round of funding is in addition to the £1.4m (around €2m) announced earlier in July to build a new secure zone for UK-bound lorries.
Last week, Eurotunnel said it wanted the British and French governments to repay the €9.7m it had invested on boosting security - and accused the authorities of "underestimating the migrant situation".
But Don Flynn, director of the Migrants' Rights Network, said: "It's not simply a matter of throwing more security, more fencing into the issue. There's a deep-rooted cause behind the problem."
Richard Burnett, chief executive of the Road Haulage Association, called for French troops to be deployed, adding that the situation was "obviously now beyond the capabilities of the French police".
When asked about the possibility of deploying British troops, Mrs May replied: "This is about ensuring we get that security fencing up, it's about working with Eurotunnel to ensure we have got the best measures in place."
Some 5,000 people, mostly from Africa and the Middle East, have set up camp around the area. From there, they often try to board trains, lorries or ferries to the UK.
Algerian Selim is one of those who tried to cross the tunnel on Tuesday, saying he wanted to work in England - a "country with a good economy" - and to see his wife and four children.
He told French TV station iTele: "The government said it's dangerous, the Channel, but me I'm going there.
"Imagine, I'm sleeping here in the jungle, I'm sleeping next to the bridge here and my kids every day are calling me, 'Daddy, when you coming?' I keep lying to my kids saying, I'm going for a job and maybe my boss is going to let me, tomorrow I'm coming. Every day I'm a liar, every day I'm lying. I'm trying," he added.
