Stowaways on an Italian cargo ship have been detained after threatening crew members as the vessel sailed close to the coast of southeast England.

Key points: Police say they do not think incident was piracy or terrorism related

Police say they do not think incident was piracy or terrorism related Grande Tema ship was coming from Nigeria, with stowaways kept in cabin for monitoring before they escaped

Grande Tema ship was coming from Nigeria, with stowaways kept in cabin for monitoring before they escaped Ship was sailing in circles off England's coast near town of Margate, with crew staying locked inside the bridge for safety

Four stowaways threatened the Grande Tema's crew, a spokesman for the boat's operator, Grimaldi Lines, said.

Grimaldi Lines said the four men had demanded to be taken to the British coast.

Police said they did not think the incident in the Thames Estuary was piracy or terrorism related, adding the four men were being held under the Immigration Act.

The men had been put under surveillance in a cabin after being discovered four days prior, but escaped.

The ship was sailing in circles off the coast near the town of Margate and its crew locked themselves in the vessel's bridge for safety.

The Grande Tema was sailing in circles off England's east coast. ( VesselFinder.com )

"The vessel was coming from Nigeria and was bound to Tilbury and those four stowaways were in the cabin," a Grimaldi spokesman said.

"Today they managed to escape from the cabin and they started threatening the crew, requesting the master of the vessel [navigate] very close to the coast.

"That request was probably because they wanted to jump and reach the British coast.

"It's a small group but obviously you can understand it would be scary."

AP/ABC