Channel Tunnel traffic came to a standstill on Saturday after a problem on a Eurotunnel shuttle train.
Eurostar, which runs high-speed trains through the tunnel between London and Paris and Brussels, said its services were not moving.
"We are a standstill due to a problem that has been reported on a Eurotunnel shuttle train. But none of our trains are actually in the tunnel at the moment," a Eurostar spokesman said.
Kent Fire and Rescue Service said a train was halted after a fire alarm sounded.
A spokeswoman said crews were mobilised to the scene, inside the tunnel, at 7.17am but there was no fire.
She said crews were at the scene and were making sure the area was safe.
Eurostar said later: "We expect Eurotunnel to allow us to start services again later this morning."
The incident comes five months after passengers were caught in travel chaos when broken-down Eurostar trains were stuck for hours in the tunnel.