At least 25 migrants were found in a refrigerated container on a boat sailing to Britain by Dutch ferry crew on Tuesday, forcing the vessel to return to port in the Netherlands, according to police and emergency services.

The stowaways received medical attention at the port of Vlaardingen, near Rotterdam, with two being transferred to hospital for more care, police said.

Taking to Twitter, Rotterdam region emergency services tweeted, “Onboard a ship it turned out that several people were found in a cooling container. The ship returned to the harbour”.

“The 25 people were taken off the ship and given the medical care they need. Earlier the message came from the ship that no people died.” Police dogs were searching the ship, which was originally bound for the British port of Felixstowe, to check that no more migrants were on board, they added.

The migrants were aboard a Britannia Seaways ferry owned by Danish operator DFDS that had just embarked on a run across the North Sea to Felixstowe in southern England.

In October, 39 bodies were found, all believed to be Vietnamese migrants, were discovered in the back of a refrigerated truck near London.

Two people have been charged in Britain and eight in Vietnam over the deaths. The container in which the bodies were found had arrived on a ferry from Zeebrugge in Belgium.