Seven people, believed to be Albanian, have been arrested after a cargo ship was brought in to port in Dorset.
The ambulance service was told a person was in need of medical attention on board the Chise Bulker in the early hours of Tuesday.
But police subsequently discovered there were seven unidentified people on the ship and none needed medical help.
The Panamanian-registered bulk carrier was brought in to Portland and the people were escorted from the vessel.
Dorset Police said the ship's crew were being questioned but there were no reports of any injuries to either the crew or the detainees.
A force spokesman said police had been contacted by the ambulance service at 05:40 GMT when the ship was off the south coast.
He said: "Officers liaised with the Border Force, the vessel's crew and other partner agencies and arrangements were made for the vessel to safely dock at Portland Port.
"A total of seven individuals - believed to be Albanian nationals - were arrested by police and escorted from the ship. They will be considered by the Border Force and UK Visas and Immigration for potential offences."