Oil giant Royal Dutch Shell has said it is working to stop a leak at one of its North Sea oil platforms.

The company would not say how much oil may have been spilt from the Gannet Alpha platform though it said it had "stemmed the leak significantly".

One of the wells at the Gannet oilfield has been closed, but the company would not say if production was reduced.

The company says it has sent a clean-up vessel to the location and has a plane monitoring the surface.

The leak was found in a flow line connecting an oil well to the platform.

"We can confirm we are managing an oil leak in a flow line that serves the Shell-operated Gannet Alpha platform. We deployed a remote-operated vehicle to check for a subsea leak after a light sheen was noticed in the area," said a Shell spokesman.

"We have stemmed the leak significantly and we are taking further measures to isolate it. The subsea well has been shut in, and the flow line is being de-pressurised," he added.