One of London's busiest tube lines has been partially closed after a burst water pipe flooded train tracks with more than two million litres of fluid, sparking concerns that the network will be unable to cope during the Olympics.
A section of the Central line, which connects commuters with Olympic station Stratford, is now suspended between Leytonstone and Bethnal Green.
A Thames Water spokesperson said workmen had bungled a pipe repair causing flooding.
"We are currently working really hard to repair a pipe that has burst in Wick Lane causing disruption to the Central Line.
"We're really sorry for the disruption this is causing."
Passengers were led through flooded tunnels after being trapped underground for two hours on Wednesday night.
The chaos has renewed fears London's transport will not cope with extra passengers during the Olympics.
London Underground's chief operating officer Howard Collins told the Evening Standard: "With less than 50 odd days to go and as the person responsible for operational readiness this is obviously something we do not want to happen during the time of the Olympics."
A Transport for London spokesperson said: "A burst Thames Water main yesterday has severely flooded a Central line tunnel, affecting signalling, power and communications equipment.
"London Underground engineers have been working flat out alongside those from Thames Water to clear up after this, but the sheer volume of water means this operation could take until at least lunchtime today. We apologise for any disruption to customers' journeys and are working to resolve as soon as possible.
"We're putting on replacement buses between Leytonstone to Stratford and Mile End to Stratford, but passengers are advised to seek alternative routes – local buses and rail operators are accepting our tickets. Plan ahead and check before you travel at www.tfl.gov.uk and check out media travel bulletins."
See below for a slideshow of tweets' concerns about the broken line.