Twenty-five people have been discovered on board a ferry travelling from the Netherlands to the United Kingdom, a spokesman for the Rotterdam Police told CNN on Tuesday.

According to the spokesman, the people were discovered by the ship's staff and seemed initially to be in “rather good condition” despite showing signs of having been in a cold environment for an extended period of time. He could not say if they had been travelling inside a cooling container.

The ferry departed from Vlaardingen, a small city on the outskirts of Rotterdam which is home to Europe's largest port.

Emergency services were called to tend to the people discovered aboard the ferry, the spokesman also said. At least 30 ambulances, 20 fire trucks and dozens of police personnel were on the scene.

The discovery comes nearly a month after thirty-nine Vietnamese nationals were found dead inside a refrigerated trailer in southeastern England, putting a spotlight on human trafficking.