Dozens of offshore workers have been evacuated from a Shell platform in the North Sea after a gas leak.

Around 50 non-essential staff were taken off the Gannet Alpha platform after natural gas began escaping underwater.

Another 28 staff remain on board but production has been shut down on the installation located 112 miles east of Aberdeen.

The Health and Safety Executive is investigating the incident which began on Monday when a sheen was spotted on the surface of the water.

A Shell spokesman said: "Shell can confirm that a release of natural gas occurred beneath the Gannet Alpha platform on the afternoon of Monday, 6 February 2012.

"The platform was successfully down-manned of all non-essential personnel as a precaution on Monday evening.

"The relevant authorities - HSE, coastguard and the Department of Energy and Climate Change - have been informed and an investigation is underway into the source and cause of the gas release.

"The shut down on the platform has been completed."

The Shell platform suffered two oil leaks last year.

More than 220 tonnesm, or 1300 barrels, of oil leaking into the sea following the leak in August.

IN DETAIL

• Second oil leak discovered on North Sea platform