The search for three crew members feared dead after a tug capsized in heavy fog on the River Clyde has been called off for the night.
The men are boat skipper Stephen Humphreys, 33, engineer Robert Cameron, 65, and crew member Eric Blackley, 57. All live in the west of Scotland.
A fourth man, aged 37, was pulled out of the river after being spotted in the water and was taken to hospital.
Clyde Coastguard said the search will resume at first light on Friday.
The Flying Phantom tug ran aground while towing a ship and capsized near Clydebank at 1810 GMT on Wednesday.
Rescue efforts for the remaining three crew members had been hampered by thick fog, with visibility at just 15m.
The temperature in the river fell to only 2.5C and survival time in the water, which has a depth of about 10m, was said to be between two-and-a-half and three hours.
Insp Louis Jeffrey, of Strathclyde Police, said earlier on Thursday that the search was now a recovery operation rather than a rescue.
He said: "Given the passage of time, the operation is now being treated as a recovery operation for practical policing purposes."
Mr Humphreys is from Greenock and Mr Blackley from Gourock, both Inverclyde. Mr Cameron is from Houston, in Renfrewshire.
Eric Blackley, Stephen Humphreys and Robert Cameron are missing
Two orange buoys marked the location of the sunken tug on the river near the former John Brown shipyard, close to the mouth of the River Cart.
Tugs and smaller vessels, including Glasgow City Council's St Mungo boat that normally cleans the river, searched in the shadow of the Titan crane.
Police officers in fluorescent jackets could be seen searching both sides of the river bank on Thursday while divers carried out a fingertip search of the tug in almost total darkness.
Clyde Coastguard sector manager Ian Plater confirmed that a number of vessels had resumed the search shortly after 0700 GMT on Thursday.
He said: "Most of the units who took part in the search on Wednesday night came back at first light this morning.
"We are still in a recovery phase and we have deployed search teams up and down the river banks.
"We still have no idea what went wrong and I would not like to speculate on the cause of this incident."
Mr Plater said weather conditions on Thursday were "slightly better today but still extremely cold".
"Last night at midnight the water was just two degrees above freezing. It's probably not much more above that now," he added.
"We've far exceeded the survival time of anybody that was in the water last night. But with search and rescue we never say never."
The section of the river where the tug capsized has been closed to commercial shipping.
The Flying Phantom helped tow the QE2 on the Clyde in September
Rescuers said a helicopter was unlikely to be drafted in to help with the search because of foggy conditions and the area's proximity to Glasgow Airport.
The alarm was raised when two community safety officers, Brian Torrie and Charlie Ayre, heard the fourth crew member shouting for help from the water and dialled 999.
Four coastguard rescue teams, three RNLI lifeboats and other boats joined the search along with Royal Navy and Strathclyde Police divers and Strathclyde Fire and Rescue.
The crewman who managed to swim for shore was rescued from the water by a passing boat and taken to the Western Infirmary in Glasgow for treatment, where his condition was described as "comfortable."
The Flying Phantom, which is owned by Danish firm Svitzer and based at Greenock, was on towing the Panama-registered bulk carrier Red Jasmine along with two other Svitzer tugs, the Mallaig and Warrior III.
It is understood no mayday call was sent out. The tug went down beside Rothesay Dock, near Clydebank College.
A spokesman for port operators Clydeport said: "As part of normal procedure a full assessment, including examination of a detailed weather forecast, was undertaken prior to the movement of the Red Jasmine upriver."
The 124ft Flying Phantom was built in 1981 and has been operated by Svitzer since 2001.
The Flying Phantom was involved in a collision almost exactly seven years ago when it hit an Egyptian cargo vessel carrying 1,000 tonnes of fertiliser in thick fog. On that occasion its four-man crew was rescued by coastguard teams.
The incident happened on 28 December 2000 on the Clyde near Clydebank, close to the site where it capsized on Wednesday.
The tug helped guide the QE2 as it arrived at the Ocean Terminal on the Firth of Clyde in September.
Svitzer managing director James Curry said: "This has been a tragic accident. We are maintaining constant contact with the families of all four crew members and keeping them informed of all developments."
Svitzer UK will be carrying out its own investigation into the accident and said it would be co-operating fully with the Marine Accident Investigation Branch of the Department of Transport.
The Red Jasmine, which has a gross tonnage of 39,000 and was carrying maize and soya from Brazil, is a Panamanian-registered vessel. It docked safely at the King George V Dock a short time after the incident.