BW Offshore Chief Financial Officer, Staale Andreassen, told Reuters that the ship was undergoing maintenance when the attack happened.

None of the people left on the vessel were injured as of last week when the attack occurred. 

“We are working now with the Nigerian authorities to get those nine people safely back,” Andreassen said.

The Sendje Berge ship is a floating production, storage and offloading vessel (FPSO) that can produce about 50,000 barrels of crude oil per day.

The ship was from the Okwori oilfield operated by Addax Petroleum, a part of China’s Sinopec Group.

A maritime security firm Dryad Global, said the attack involved three boats and explosives.