The London Underground drivers union has announced drivers will stage another 24-hour tube strike, from 9.30pm on August 5, as the dispute over the new all-night tube continues.
The decision to stage another strike came as both sides in the dispute were invited to hold fresh talks in a bid to avert a repeat of last week's industrial action.
Unions are unhappy about pay and rosters for the new service, which is due to start on September 12.
Old Routemaster buses were in operation around the capital today as Transport for London attempted to keep London moving during the Tube strike.
TfL said there was a record number of buses on the capital's roads after 266 extra buses were brought in for the first day of the 48-hour walkout.
David Cameron described travel disruption caused by the Underground strike in the capital as "unacceptable" on Twitter.
A 48-hour Tube strike has created "total chaos" for Londoners just trying to get to work, one commuter has said.
Emily Toner told ITV London that she was forced to hire a Boris bike because of the crowds at Liverpool Street station:
The RMT union said its members were forced to take industrial action as London Underground "have refused to move one inch" over ticket office closures and claimed the operator had breached an agreement the groups had previously reached through Advisory, Conciliation and Arbitration Service (Acas).
A 48-hour strike by London Underground workers began this morning, causing widespread disruption for commuters in the capital.
Members of the Rail, Maritime and Transport union (RMT) started a 48-hour strike at 9pm last night over a long-running dispute about plans to close Tube ticket offices.
The union says the closure of ticket offices will cost hundreds of job losses and threaten safety, while LU says staff would be better employed on station concourses as only 3% of tickets are bought at ticket offices.
Normal underground services will resume tomorrow night at 9pm before a a three-day stoppage from 9pm next Monday.
Boris Johnson has hit out at senior members of the RMT union over the 48-hour strike on London Underground.
The Mayor of London said the strike was only happening because some "union barons" were trying to "flex their muscles" in a bid to succeed former leader Bob Crow, who died in March.
Leader of the RMT Bob Crow said the tube strike will go ahead after talks between London Underground bosses and the union failed to reach an agreement over pensions.
He said: "The action next week remains on and it is the management's intransigence that is responsible for the disruption travellers can expect."
No further talks between leaders of the RailMaritime and Transport (RMT) union and London Underground leaders have beenarranged, raising the threat of disruption to Tube services next week.
Earlier this week RMT officials said its members will walk out at 4pm on Tuesday until the same time on Friday.