Traffic was suspended in the between Britain and France on Saturday after smoke was detected, according to the Eurotunnel firm that operates it.
“Due to an incident in the tunnel, all departures are currently suspended in both directions,” Eurotunnel said on its Twitter feed.
The Eurostar passenger train service said on its website that all services had been cancelled for the day.
All trains already en route were forced to turn back to their stations of origin.