At least six hostages have escaped from a Nigerian oil facility that armed men took over earlier this week.

Officials for the Italian oil company Agip said Thursday that the workers managed to run away from the facility and made their way through creeks and swamps to safety.

The armed men are still holding about 40 other workers hostage at Agip's Tebidaba oil pumping station in Bayelsa state. Local officials are negotiating for the workers' release.

The Associated Press quotes a local police official as saying the hostage-takers are seeking a ransom of $75,000.

Hostage-takings and kidnappings are common in southern Nigeria, where most residents live in poverty despite the billions of dollars the government earns in oil revenue.

Militants have stepped up a campaign to give local communities a greater share of the region's oil wealth.