Four men have been detained under the Immigration Act after police boarded a cargo ship amid reports of stowaways threatening crew.
Essex Police said the vessel, in the Thames Estuary, was boarded at around 11pm on Friday and was taken to the Port of Tilbury in Essex.
It arrived at just after 4.20am on Saturday, according to MarineTraffic.com.
The ship's operator, Grimaldi Lines, said four stowaways had been found on board and were armed with iron tubes.
They were said to be calling on the crew to navigate closer to the coast.
The force was called at around 9.15am on Friday relating to the safety of the crew on board the Grande Tema, a 71,000-tonne ship which set off from Lagos, Nigeria, on December 10.
Paul Kyprianou, a spokesman for Grimaldi Lines, told Sky News on Friday morning: "We found four stowaways on the vessel.
"The vessel was coming from Nigeria and was bound to Tilbury, and those four stowaways were in the cabin, and today they managed to escape from the cabin and they started threatening the crew, requesting the master of the vessel navigating very close to the coast.
"That request was probably because they wanted to jump and reach the British coast.
"The crew reacted and they locked themselves in the bridge of the vessel and so they are safe, we haven't had any injuries."
The force said the ship was secure and there were no reports of injuries.