Eight people have drowned after the sinking of a hijacked ship held by pirates off the coast of Somalia since November 2010.
At least six pirates and two crew members died, according to the European Union Naval Force.
It said the Malaysian-flagged MV Albedo was still under pirate control when it sank on Sunday.
The EU Naval Force was helping in the rescue operation.
Hassan Abdi - a pirate commander in Hobyo, a rebel stronghold in coastal central Somalia - said the vessel sank after having experienced mechanical problems for months.
He gave the casualty figures and said two crew members also were rescued.
The EU Naval Force said the vessel originally had 15 crew members and that a search for other survivors was under way.