A major emergency response is under way after a tug boat sank off Greenock on Friday afternoon.
Emergency crews were called to Custom House Quay just before 3.30pm, after the tug flipped over.
Images from the scene showed rescuers in inflatables and a police boat surrounding the capsized boat.
It is not known how many people were on board, or if there have been any casualties.
Eyewitnesses reported seeing the boat, which was one of two escorting a civilian vessel into the harbour, flip and capsize.
They added that a lifeboat crew was seen banging on the upturned hull of the stricken vessel, just before it sank minutes later.
Police confirmed that officers were in attendance at the scene.
A Coastguard spokesperson said: “HM Coastguard is currently responding to reports of a capsized vessel at Custom House Quay in Greenock, February 24.
“Just before 3.30pm Coastguard Rescue Teams from Helensburgh and Greenock, a lifeboat from Helensburgh and the Coastguard helicopter from Prestwick were sent to assist and are searching the area.
“Police Scotland is also in attendance.”