Pirates have seized a Panama-flagged oil tanker which was anchored in the Ivory Coast's economic capital of Abidjan, authorities said on Monday.
A statement from Abidjan port authorities said "armed individuals" hijacked the vessel ITRI on 16 January.
The ship, which was due to discharge 5000 tonnes of oil and was unable to put out a distress call in time for a rescue, has been located off neighbouring Ghana, it said.
Authorities said a crisis team has been established for the hijacked vessel and its crew, adding that "the highest military and civilian authorities" are involved in handling the case.
In October, a Greek tanker in Abidjan was hijacked by pirates who looted the vessel before releasing it.
Piracy attacks in west Africa have mostly taken place in Nigeria, Africa's largest oil producer, but they have recently increased in the waters off Benin.