A MAJOR emergency rescue operation is under way after a boat sank off East India Harbour in Greenock.

The alarm was raised around 3.30pm.

Onlookers at the scene said that they could see a lifeboat crew tapping on the upturned hull of the stricken vessel before it sank just minutes later.

READ MORE: EYE-witness of incident on the Clyde says they thought the terrifying ordeal was a 'training exercise'.

One Twitter user posted from the scene: 

Police, coastguard crews and a search and rescue helicopter are all on the scene.