Shell confirmed Friday afternoon that an oil leak had occurred in a flowline serving the Gannet Alpha platform in the U.K. North Sea.

Shell spokesman Kim Blomley said, "We have stemmed the leak significantly and we are taking further measures to isolate it," he said. "The subsea well has been shut in, and the flow line is being depressurized. We continue to monitor the situation on the surface and subsea."

Shell has informed the Maritime & Coastguard Agency, the Department of Energy & Climate Change (DECC) and the Health & Safety Executive.

Spokesmen for the DECC and the Maritime & Coastguard Agency have responded to the incident and are investigating the situation. "It doesn't appear to be a big oil spill," said DECC spokesman Jonathan Farr.

The Gannet Alpha platform is located 180 kilometers east of Aberdeen in central North Sea. Shell operates the platform along with ExxonMobil's U.K. unit Esso.