A Devon lifeboat was called out to a merchant navy ship after a man was stabbed on board.
Torbay's all-weather lifeboat is conducting a search for a man its crew believes may have gone overboard.
The search started just after 1800 GMT on Thursday when coastguards received a mayday call from the Overseas Josefa Camejo, two miles east of Berry Head.
Police confirmed that a senior member of the crew was stabbed and suffered life-threatening injuries.
Officers boarded the ship and are treating the vessel as a crime scene.
An RNLI lifeboat crew and a helicopter from RAF Chivenor are assisting with a search of the area for the man thought to have gone overboard.