Six crew members from a German-owned container ship, including the captain, are currently at the beck and call of strangers.
They were kidnapped in Port Harcourt, the Rivers State capital, maritime security operatives said.
The Sea Guardian consultancy said the Demeter “was attacked by pirates” at about 7:00 am (0600 GMT) on Saturday.
“Pirates boarded the ship, kidnapped six crew, including (the) master, chief officer, second officer, second engineer, bosun and cook,” it said.
The Demeter had been travelling from the capital of Equatorial Guinea, Malabo, to the Liberian capital Monrovia at the time.
The Liberia-flagged vessel is owned by German shipping firm the Peter Doehle Group.
The MTI Network, a crisis communications firm that deals with incidents in the shipping industry said the attack happened as the ship entered the port of Onne.
“All of the 12 remaining seafarers of the Demeter are safe and unhurt and the vessel has proceeded to safe waters,” it said in a statement.
The Peter Doehle group said it would not disclose the nationalities of the crew members taken “for security reasons”.