Pirates kidnapped 12 crew members from a Swiss merchant vessel on Saturday in Nigerian waters, the ship's operator said in a statement.

Kidnapping for ransom is a common problem in parts of Nigeria. A number of foreigners have been kidnapped in the last few years in the southern Niger Delta region, source of most of the crude oil which is the mainstay of West Africa's biggest economy.

Massoel Shipping, operator of MV Glarus, said the vessel carrying wheat was travelling between the southwestern commercial capital Lagos and southern Niger Delta oil hub Port Harcourt when it was boarded by pirates, who took away 12 of the 19 crew members.

It said the attack happened around 80 kilometres southwest of Bonny Island.

"The company is working with the authorities and specialists to secure the speedy and safe release of those being held," Massoel Shipping said in its statement. The statement did not give the nationalities of the crew members.

A naval officer mans a machine gun on a boat off the Atlantic coast in Nigeria's Bayelsa state Dec. 19, 2013. (Stringer/Reuters)

Switzerland's foreign ministry said it had learned from the company that none of the crew members were from Switzerland itself.

Nigeria's navy and maritime police said they were unaware of the kidnapping and would investigate.