Smoke detectors were set off by a "smouldering load" in the trailer of a lorry, it said, clarifying an earlier statement in which it had said the source of the smoke was unknown.
"The smouldering has now been dealt with by the fire and rescue services, and we are now working to remove that shuttle and to get services restarted again in the other tunnel this evening," a spokesman for Eurotunnel told Reuters.
A full service in both tunnels was likely to begin again on Sunday, he added, with no information on what the smouldering load was at this stage.
British police had earlier said the tunnel closure was due to a lorry fire and the Calais-Dover shuttle train had been evacuated due to the smoke. There were no injuries.
"Rail passengers are advised to expect significant delays whilst the vehicle is being recovered and fumes are cleared from the tunnels," Kent police said in an emailed statement.
Eurostar, the operator of passenger train services through the tunnel between Paris, London and Brussels, said on Twitter its passenger trains would not be running on Saturday and that all trains halted en route would return to their original stations.
It advised passengers to postpone journeys and not come to stations.
France has been on high alert since Islamist militants killed 17 people in three days of violence in Paris that began on Jan. 7 with an attack on the offices of a satirical newspaper.