Pat Adamson, a spokesman for Pioneer Ship Management Services, said the company has not had contact with the crew since a distress message said the pirates had boarded the ship during the night. Crew members are unharmed and believed to be locked in a panic room aboard the ship, Adamson told Xinhua news agency.
No ransom demands have been made by the pirates and the shipping company has not made contact with them.
"Pioneer is taking the matter extremely seriously and its primary concern is for the well-being and safe return of its crew members," Adamson said.
The ship is off the coast of Lagos, Nigeria's shipping hub. Frequent pirate attacks in the region have been a hindrance to trade, Xinhua reported.