Nineteen people working overnight in the Channel Tunnel have suffered carbon monoxide poisoning on the job, with one in a serious condition, French officials have said.
Around 60 workers were changing tracks on the line which connects Folkestone with Calais when the incident happened.
The seriously affected welder was diagnosed with carbon dioxide poisoning after being taken ill in the early hours of Sunday morning.
18 others, whose condition is not cause for great concern, were also taken to local French hospitals after becoming unwell to give them time to "remove the carbon monoxide from their system," an official said.
The remaining workers were sent home and an investigation has been launched.
John Keefe, director of public affairs at Eurotunnel Group, told Kent Online: "Detectors in the tunnel didn't show excess levels of carbon monoxide.
"A number of workers were taken into hospital for medical observation as a precaution and Eurotunnel is monitoring their condition carefully."