Commuters and tourists in London face a day of travel chaos because of a strike which has closed the underground.
Tube services ground to a halt on Wednesday evening and will not resume until Friday.
Members of four unions are taking industrial action for the second time in a month because of a deadlocked dispute over plans to launch a new all-night service next month.
Extra buses will be laid on, but there will be huge disruption and London's roads could be gridlocked if people switch to cars.
Picket lines will be mounted outside Tube stations, which will be closed all day.
The dispute over pay and conditions for the planned night Tube has worsened in recent days, with more workers being balloted for action and London's mayor making it clear no more money will be offered.
Staff on the Docklands Light Railway, London Overground, the bus network, tram and TfL Rail services are not on strike.
These services will run as normal, but they will be much busier than usual and people were strongly advised to travel outside of the morning and evening peaks.
TfL will have more than 600 "travel ambassadors" on hand to help Londoners, visitors and tourists get to their destinations on foot, by bus, bike or other means.
Around 250 extra buses are being provided and there will be more river services.
Mayor Boris Johnson said he was "not fussed" about the new service starting on time on September 12.
"I want it starting in the autumn - what I am fussed about is the offer being put to union members.
"I am not going to authorise any more money. Most people would recognise that this is a very generous deal. "
Aslef general secretary Mick Whelan said: "Our members have rejected the latest offer from the company because they are forcing through new rosters without agreement and offer no firm commitments on work life balance for train drivers."
RMT leader Mick Cash said: "The offer tabled by London Underground is just a rehash ?of an earlier package and does nothing to tackle the fundamental issue of our members being called into work at the beck and call of management to plug staffing gaps in the mayor's botched night Tube plans."
Steve Griffiths, LU's chief operating officer, said: "We have made every effort to reach agreement with the unions and avoid this unnecessary strike action. On the table is an extremely fair offer."