The pirates stormed the vessel in the Gulf of Guinea, an area that has seen a sharp spike in the number of reported marine attacks over the last six months.
A spokeswoman for Sea Trucks Group, which provides support vessels to oil companies operating in Nigeria, told AFP that one of the company's ships came under fire and that the firm's employees were taken in the raid.
"At this time Sea Trucks Group is making every effort to ascertain the whereabouts of its personnel," the spokeswoman, Corrie van Kessel, told AFP.
Nigeria's navy spokesman Commodore Kabir Aliyu said during the attack "four expatriates are reported to have been kidnapped from the vessel; two sailors were killed."
He said those kidnapped were from Indonesia, Iran, Malaysia and Thailand.
The attack, which also left two other seamen injured, took place at roughly 0100 on Saturday, 35 nautical miles off Nigeria's oil-rich Niger Delta coastal area, the navy and company said.
Aliyu told AFP that the motive of the attack had not yet been established and that so far there has not been any communication with the gunmen.