French authorities say about 50 migrants attempted to scurry aboard a cross-Channel ferry that had arrived from Dover, England into the northern French port of Calais late Saturday.
Officials say 44 of the refugees were apprehended, dashing their hopes of reaching England on the vessel's return trip.
Two of the migrants fell into the water, but were quickly rescued.
Maritime officials say ferry traffic was delayed for several hours as police searched the ship.
Authorities say at least 100 migrants stormed into the port Saturday night.
The French news agency, AFP, reports that police were continuing to look Sunday morning for a least four more migrants the police believed were still hiding out on the same ship where the other migrants had been apprehended.