A London Underground line ground to a halt today after a cement leak damaged a signal control room.
The Victoria Line was closed between Warren Street in the centre of the capital and Brixton in the south after the leak from an area where contractors were working on a long-term upgrade of Victoria Station.
It left tens of thousand of rush hour commuters searching for an alternative way to get home, with Transport for London saying the line would be affected for the rest of the day.
Nigel Holness, London Underground's operations director, said: "This afternoon our contractors were working on the new station in an area next to the Victoria line signal control room.
"These works involved the use of water and cement which leaked into the room, damaging equipment.
"This has meant there are no signals working on the southern section of the line.
"Our engineers are working hard to resolve the situation as soon as possible to get services back up and running, but the line is expected to be affected for the remainder of the day while repairs are carried out."
Passengers were initially told the closure was due to "flooding" at Victoria Station.
But pictures were later posted on the UsVsth3m website purporting to show a layer of cement in the affected room.
Passengers are being advised to use the Northern and Bakerloo lines. Replacement buses are also running between Green Park and Brixton.
A spokesman for the RMT union said: " We understand that a foot of concrete burst into the control room, having been poured into an escalator void.
"We await further information but what we do know is that LU technicians are on site now, working flat out to clear up the mess and get services back on line, proving once again that it's directly-employed public sector staff who are needed to deal with this kind of emergency, making a nonsense of Boris Johnson's Tube staff cuts plans."