The three Moroccan nationals were found on the ship after border police received the tip-off about possible stowaways. Harbour police and coastguard boats were also used to search the waters around the vessel.
According to border police spokeswoman Marloes de Ridder, it was not clear how the three men had managed to evade detection during routine checks of the lorries boarding the ferry. She said they suspected that the men had jumped from a trailer while they had been on board.
The migrants are currently being detained while police investigate the way they traveled to the port.
Image: Port of Harwich (England)
The number of people attempting to travel illegally from Hook of Holland has sharply increased in recent years. Since the beginning of 2019, a total of 450 people have been intercepted onboard ferries, 80 of whom reached the port in Harwich. Human trafficking gangs are suspected of being behind the increase.