The first London Underground strike shutdown since 2002 got underway on Wednesday, as drivers protested pay and plans for a new 24-hour service due to start in September.
Commuters rushed home ahead of the start of the strike at 6:30 pm (1730 GMT), as unions mounted picket lines outside stations and Transport for London (TfL) began reporting delays.
A full shutdown is expected on Thursday, and TfL has warned that disruptions to the British capital's public transport could continue into Friday.
Transport for London (TfL), the local government organisation responsible for most aspects of London's transport system, said it would lay on 200 extra buses and more bicycle rental hubs, although it also posted walking maps of London on its website.
"Londoners who own a bike are encouraged to cycle to work," the network administrator said in a statement.
To reach the Wimbledon tennis tournament, which ends this weekend, TfL said it was organising a taxi-sharing service from the nearest train station.
"We're very clear that it's unacceptable and unjustified. It's going to hit families, workers, businesses across the capital," Prime Minister David Cameron's spokeswoman said at a daily briefing.
London Mayor Boris Johnson tweeted: "Tube strike politically motivated - union bosses need to explain why they refuse to put new offer to members - disgraceful - call it off!"
New all-night Underground services are due to start in September on several lines and staff have been offered an average 2.0-percent pay rise this year, inflation-linked rises for the next two years and a £2,000 bonus for each driver on the new overnight service.
This offer was rejected by unions on Wednesday.
London Underground's managing director Mike Brown said an all-night Tube service would support jobs and boost the city's economy, adding that the offer had been "remarkably fair".
But Finn Brennan of the Aslef trade union accused managers of playing "foolish games of brinkmanship".