London: London Underground staff walked off their posts on Wednesday to protest plans to run Tube trains all night at weekends, the second shutdown of the British capital`s subway in under a month.
The strike began at 6:30 pm (1730 GMT) and will run until Friday morning, causing disruption for millions of commuters and tourists.
The action brought forward the London rush hour on Wednesday as commuters squeezed into stations in order to get home before the strike kicked off.
It will also hit football fans travelling to see English champions Chelsea host Italian side Fiorentina in a friendly game at Stamford Bridge on Wednesday.
Overground trains and buses were to run as normal.
The action comes less than one month after the four main trade unions staged a similar strike on the world`s oldest subway system, which handles up to four million journeys every day. It was the first complete shut down of the system in 13 years.
Unions are locked in a bitter dispute with Tube operator London Underground over plans to run trains through the night on Friday and Saturdays from September 12.
After talks broke down again on Monday, union leaders called for the launch of the new service to be postponed until a deal can be reached about staff pay and work conditions.
Mick Cash, leader of the RMT union, said the all-night service was "rushed and botched from the off", and said it would now ballot more workers for industrial action.
London Mayor Boris Johnson said however that staff have already been offered a "generous" package that would not see anybody working more hours than they do at the moment.
He rejected suggestions that the night Tube was a populist measure that would only benefit partygoers, saying it was also aimed at the city`s many shift workers who must currently endure lengthy journeys by bus.
"These are not party animals, not just people going home after a night out, they are the working people of London," the mayor told BBC radio.
Steve Griffiths, London Underground`s chief operating officer, added: "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."
Current timetables vary depending on the line but trains begin in the outer edges of London some time after 5:00 am and the last services leave the centre about half past midnight.
From September, trains will run 24 hours on Friday and Saturday on five of the 11 underground lines, bringing London in line with other cities such as New York, Berlin and Sydney.