According to unconfirmed information, this is an attempt to take over an oil tanker.
A local radio station on the Isle of Wight reports that the incident is taking place aboard the Liberia-registered oil tanker Nave Andromeda, which left Nigeria last week and which would have docked at the port of Southampton on Sunday.
The British Coast Guard announces that rescue helicopters have been sent to the ship, reports Reuters.
British media, including Sky News, have reported that these are free passengers trying to take over the ship.