Authorities have found 25 migrants stowed away on a cargo ferry bound for Britain shortly after it left the Netherlands and the vessel quickly returned to the Dutch port of Vlaardingen, emergency services say.

Two of the migrants were taken to hospital for treatment while the other 23 received a medical check-up in the port before being taken away by police for processing, a statement said on Tuesday (local time).

Authorities found the migrants in a refrigerated container aboard the ferry. Sniffer dogs were being used to comb the vessel for other possible stowaways, it said.

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.

On Oct. 23, 39 bodies, 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.