A bomb squad and dog unit has arrived at Joliette and they are investigating the cause of the explosion.
A senior police officer told local media: "The boat does not leak, so we do not understand what happened. It is not known if the explosion was held on the ship."
The heightened risk of a terrorist attack across the Channel comes after the Bastille Day lorry attack in Nice, which killed 84 people and the execution of a priest in a Normandy church.
The French president Francois Hollande said he would increase armed security at transport hubs and crowded areas, but the appearance of soldiers at Calais is said to have shocked British authorities.