Statoil confirmed Tuesday production from the Snorre B platform closed Saturday after the "discovery of an abnormal erosion of mass under the template [of the platform]."
Snorre is Norway's fourth-largest field. The Snorre B platform started production in 2001.
The company said the area under the platform is under constant surveillance. There have been no indications of any hydrocarbons leaking since the anomaly was discovered.
"The pit is stable and is being monitored continuously," Bente Aleksandersen, a senior vice president for regional operations, said in a statement. "The most important thing for us now is to clarify what caused the pit to form, and a number of explanations are being examined."
The company said it pulled more than 30 people from the platform as a security precaution. Statoil said the platform will remain shut down while investigations continue in coordination with Norway's petroleum safety authority.