Suspected Nigerian militants seized several oil industry workers as hostages in a raid on a boat on Wednesday, industry and security sources said.
One source said the deep water vessel was operated by Italian oil company Saipem, a unit of ENI, and staffed mostly by foreigners.
"Some armed men came in several boats this morning to a facility in deep water and took everyone hostage," said a security source in the oil industry, asking not to be named.
"Right now the entire facility is under siege and several expats have been taken because the facility is being maintained by expats."
Dozens of mostly foreign oil workers have been kidnapped in Nigeria this year as ransom-seekers have taken advantage of instability caused by growing militancy in Nigeria's deep south.
Almost all have been released unharmed after payments, although one Nigerian oil worker was killed in August by troops during an attempt to free him.