Updated

Pirates attacked a Chinese fishing vessel in a rare attack off West Africa, officials said Thursday.

Four of the pirates, all from neighboring Guinea, were killed early Wednesday in a clash with the Sierra Leone navy, police spokesman Mohamed Samura said. Two were shot and another two drowned, he said. The remaining four were arrested.

The pirates approached the Shanghai 3 before dawn off Yeliboya, a coastal town between Freetown, the capital of Sierra Leone, and Conakry, the neighboring capital of Guinea.

"They boarded the vessel and put everybody on board — both Chinese and Sierra Leoneans — under gunpoint," said Idriss Conteh, the secretary of the AFRIC fishing company, the local agent that was using the vessel.

"They entered every cabin and took away personal effects including money and then asked the crew to move to the cold room and asked the crew to load all their fish stocks into the pirates' boat," he said.

Once the pirates left, the Shanghai 3 radioed for help. Its sister vessels answered the call and caught up with the pirates' boat, which was traveling slowly due to its heavy load. When the navy arrived, the pirates opened fire, said Conteh.

During the scuffle, the pirate's boat collided with one of the sister vessels and began to sink, at which point, the pirates surrendered, he said. Onboard, security forces discovered an AK-47 and several rounds of ammunition.

Piracy has become increasingly common off the coast of Somalia in East Africa. With the exception of some attacks on oil vessels off Nigeria, it is relatively uncommon off West Africa.