The nationality of the crew was indicated on the website of the ship owners, Ancora Investment Trust Inc based in Greece.
The pirates sailed farther into the waters of Gulf of Guinea with the ship and have not yet been tracked by Nigerian security agencies, the officials said.
A security company, AKE Limited, said if the ship is hijacked, it is likely to be held by hijackers for close to a week during which they would offload the contents before releasing the ship.
Incidents of hijacking are not new to the region.
In July, assailants hijacked a Greek oil tanker with 20 crew members on board.
The ship-- 'Aegean Star'- which was released a few days later belonged to Endeavour Marine Agency based in Greece's main port of Piraeus.
Over the last few months, piracy in the region has escalated from low-level armed robberies to hijackings and cargo thefts.