A spokesman for the oil company said on Monday that its pipeline crossing the Ramos river near the fishing villages of Agge and Agoro, 350km southeast of Lagos, had been ruptured in an attack on Friday night.
The pipeline would normally carry crude oil from wells in Bayelsa State in the western delta to Shell's Forcados export terminal, but the firm's output from the area had already been shut down because of security concerns.
A spokesman for Shell said that the extent of the damage was not yet known, as an inspection has been carried out only by a helicopter overflight.
Last month, Shell suspended crude loading at Forcados terminal and evacuated the nearby EA offshore field, slashing Nigeria's 2.6 million barrel per day output by almost 20% and pushing world oil prices higher.
The shutdown followed a series of attacks by armed separatist militants fighting for a control of the delta's oil revenues. On 18 February, nine foreign workers from a Shell subcontractor were kidnapped after a brief gun battle with Nigerian security forces. Six of them were later freed, but a Briton and two Americans are still being held hostage.
Since Forcados suspended loading, several oil flow stations and pipelines have been blown up by the militants, and it is not clear how long it will take the company to restore production if the security situation improves.