"We can’t really tell what the cause of the fire is," said a resident of the town of Gio, where Ogoni indigenous people live.
Anglo-Dutch oil giant Shell on Monday shut down a major pipeline in southern Nigeria after fire broke out in its supply lines, a spokesman for the company said.
"A fire has been observed on the right of way of the Trans Niger Pipeline (TNP) at Gio in Ogoni land," said spokesman Joseph Obari.
"SPDC (Shell Petroleum Development Company) has shut the TNP as a precautionary measure pending the investigation," he added.
The TNP has been repeatedly attacked by vandals and oil thieves, and Shell said it would investigate whether the fire was the result of an attack by one of the armed groups that operate in the region.
"We can't really tell what the cause of the fire is," said a resident of the town of Gio, where Ogoni indigenous people live.
"All we know is that we came out from the house this morning only to see that the pipeline is on fire," he added.
The Trans Niger Pipeline transports natural gas and 180,000 barrels of oil per day to an export terminal at Bonny, on the south coast.
On Saturday, a group called the Niger Delta Avengers claimed responsibility for an attack on another major oil pipeline in southern Nigeria, breaking a ceasefire the militant group had declared a month ago.
Nigerian oil production has sunk from 2.1 million barrels a day in the first quarter to 1.7 million barrels in the face of repeated militant attacks.
Ratings agency Standard and Poor's cut Nigeria's credit worthiness this month, saying the drop in production and a restrictive foreign exchange regime were hurting the country's prospects.