London was braced Wednesday for the second shutdown of the Underground within a month as trade unions stage a strike over plans to run Tube trains all night at weekends.

The walk-out will last from 6:30 pm (1730 GMT) until Friday morning, causing disruption for millions of commuters and tourists.

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 will run as normal.

The strike comes less than one month after a similar action shut down the Underground network, which handles up to four million journeys every day, for the first time in 13 years in early July.

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 revellers, 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.

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 lines, bringing London in line with other cities such as New York, Berlin and Sydney.