The man, who is understood to be an Egyptian in his late teens, was trying to jump from the roof of one train onto a Eurostar train at around 2pm.
He was electrocuted and fell to the tracks below. Medics took him to hospital, where he was left fighting for his life.
A spokesperson at Eurostar confirmed that someone “was on the tracks” early on Wednesday afternoon.
(Trains were delayed on the Eurostar line at Gare du Nord. Photo: AFP)