Armed men seized a Greek oil tanker just outside the Cameroonian port of Limbe, Greek authorities said on Tuesday.
Eight people were abducted and one person — a Greek national — was injured.
The five Greeks, two Filipinos and a Ukrainian were part of a 28-member crew aboard the Happy Lady.
The vessel was 2 nautical miles (3.7 kilometers) off Limbe port when it was raided overnight into Tuesday.
Greece’s state-run AMNA news agency said the government was closely monitoring the situation.
Attacks on ships and kidnappings for ransom are relatively frequent along the West African coast.
Pirates hijack ships sometimes for several days as they pillage their cargo while demanding hefty ransoms in return for the release of the crew.
Armed men raided another Greek oil tanker, the Elka Aristote, in November around 10 nautical miles off the Togolese capital Lome, capturing four sailors.
They released three of the men on December 13, but one died in captivity.