"Peter Doehle Schiffahrts-KG are pleased to report that the six crew members of her container vessel Demeter who were taken hostage on October 21 and have spent the past two and a half weeks in captivity, were released and are now safe," the Hamburg-based group said in a statement to AFP.
"Peter Doehle Schiffahrts-KG wishes to thank all the relevant authorities for helping to secure the release of our much valued seafarers," added the statement, which did not elaborate on the rescue mission.
The group, which would not comment on the nationalities of the six, said they were in good health.
Nigerian authorities had not commented on the rescue by mid-afternoon.
The six were abducted when the Demeter was attacked by an armed criminal gang off the southeastern port of Onne.
The Liberian-registered vessel had been sailing from the Equatorial Guinean capital Malabo to Monrovia.
In a report published last week the International Maritime Bureau listed 21 incidents of maritime piracy in internationals waters, including shootings and attempted kidnappings as well as hijackings.
The Bureau cited the Gulf of Guinea off western Africa as remaining dangerous, even though incidents had fallen off elsewhere.
The IMB's director Pottengal Mukundan cited Nigeria's Bayelsa state, Bonny Island and the oil hub of Port Harcourt," as particular areas of concern.