Gunmen hijacked a vessel belonging to French oil services group Bourbon off Nigeria's Niger Delta on Sunday as it travelled towards a Royal Dutch Shell offshore oilfield, security sources said.

The vessel was carrying four expatriates from Cameroon, Ghana and Lebanon when it was attacked near the Bonny Fairway buoy, a major shipping route for the Nigerian oil services industry, one of the sources said.

"It was hijacked by gunmen in about five speedboats. The vessel lost contact with the control room around the Okwori oilfield area near Bonny," the source, a private security contractor working in the oil industry, told Reuters.

A second security contractor confirmed the vessel had been travelling to Shell's Bonga offshore field when it was seized.

Bourbon officials could not immediately be reached for a comment and no group claimed responsibility.

Piracy and kidnapping is common in the Niger Delta, a vast network of mangrove creeks opening into the Gulf of Guinea and home to Africa's biggest oil and gas industry.

Militants who say they are fighting for a fairer share of the region's natural wealth have blown up pipelines and kidnapped oil workers in a campaign of attacks since early 2006, shutting down around a fifth of Nigeria's oil output.

Criminal networks have taken advantage of the insecurity, carrying out kidnappings and hijackings for ransom. Hundreds of foreigners have been seized over the past three years, but most have been released unharmed after a financial settlement.