A search for a crew member missing after a tug capsized and sank on the River Thames in London was called off tonight as marine accident experts began an investigation into the accident.
Two other crew members were safely rescued after the tug, called Chieftain and which was towing a barge with a crane on it, went down off Greenwich Pier in south London just before 11am.
A major search-and-rescue operation was launched for the missing crewman, with efforts being co-ordinated by the Woolwich-based London coastguard.
But about four hours after the sinking the Maritime and Coastguard Agency (MCA) said the search, involving police, the Port of London Authority, the fire brigade and lifeboat crews, had been called off.
The section of the river around Greenwich Pier had been closed while the search had gone on.
The MCA said: "The Port of London Authority (PLA) is beginning the first stages of an operation to raise the sunken tug. Depending on the circumstances, this will be carried out by PLA or by a salvage contractor.
"The Marine Accident Investigation Branch have begun an investigation into the causes of the accident. The incident is also being investigated by the MCA survey and inspection branch."
At the scene of the accident, a second tug boat, which river workers said was also attached to the barge, was still afloat and activity could be seen on deck.
One onlooker said they went to the riverside shortly after the incident at 11am but by then the boat was underwater.
One passer-by who witnessed the sinking said: "The front tug seemed to hit a buoy and capsized. It was submerged within a matter of minutes. I saw two men being pulled out of the water on the other side of the river.
"All the boats in the area scrambled and were searching for the third man. As the minutes dragged on, I started to fear the worst. It was terrible watching and not being able to help."
Thames safety measures were tightened in the aftermath of the 1989 Marchioness riverboat sinking disaster in which 51 people died when their boat was in a collision with a dredger on the Thames near Southwark, south London.
The improved measures included the setting up of the London coastguard which is located at the Thames Barrier Navigation Centre at Woolwich.
Today's sinking follows the death on the Thames last week of Ben Woollacott, 19, a crewman on the Woolwich Ferry.
He fell from the ferry and under its propeller while mooring ropes were being untied.
Paramedics treated the crewman when he was pulled from the Thames, but he was pronounced dead at the scene.
He was the son of Stephen Woollacott, owner of a Thames riverboat company.
Transport for London said today the Woolwich Ferry will be suspended on Monday as staff will be paying their respects at Mr Woollacott's funeral.
Thames River Services and Crown River Cruises are also suspending services on Monday.