London Underground workers have launched a 24-hour strike which will cripple Tube services and cause travel chaos for millions of passengers.
Members of the Rail, Maritime and Transport union and the Transport Salaried Staffs Association walked out at 6pm in a long-running dispute over jobs and ticket office closures.
They rejected a last minute offer from Transport for London as well as a plea from Mayor Sadiq Khan to call off the action.
The unions say over 800 jobs have been axed as ticket offices closed, claiming staff are being abused by passengers facing queues at ticket machines.
TSSA reps rejected the latest offer, following an earlier decision by the RMT.
General secretary Manuel Cortes said: "Whilst they accept the offer of more staff is a step in the right direction to restoring Tube safety standards, they do not believe the offer will return those standards with the urgency that is now needed.
"We remain committed to taking part in further talks to seek a resolution to this dispute."
RMT general secretary Mick Cash said in a message to union members: "Despite the best efforts of your negotiators over many days, London Underground has not put forward acceptable proposal to address the staffing and safety issues."
Transport for London (TfL) advised passengers there will be a severely reduced service across the Tube network all day on Monday because of the strike.
The RMT said over 800 jobs had been axed under the so-called Fit For The Future programme, adding that London Underground was only offering to reinstate 150.
Most of the 500 new jobs claimed by the company were to fill current vacancies and staff turnover, according to the union.
Mr Khan said: "This strike is going to be a huge inconvenience to commuters, tourists and TfL staff, and it is pointless.
"There is a good deal sitting on the table that will ensure station safety and staffing levels across the Tube network. I am willing to carry on negotiations.
"This historic dispute has nothing to do with the millions of Londoners this strike is punishing. It must be called off."
TfL said it will try to run as many services as possible but passengers were told that most Zone 1 stations are likely to be closed throughout the action.
National Rail services will not be affected by the strike but there will be no Underground services from key interchange stations such as Victoria, King's Cross, Waterloo, Paddington, Euston, Bank and London Bridge.
Piccadilly line services will run between Hammersmith and Heathrow Terminals 1, 2 and 3, but there will be no service to Terminals 4 or 5.
There will be no service at all on the Victoria or Waterloo & City lines, and all other lines will be severely affected, with limited services in outer London.
Steve Griffiths, chief operating officer for London Underground, said: "There is no need to strike.
"We had always intended to review staffing levels and have had constructive discussions with the unions.
"We agree that we need more staff in our stations and have already started to recruit 200 extra staff and that is likely to increase further as we work through the other areas that need to be addressed.
"Taking into account existing vacancies and natural turnover this means that over 600 staff will be recruited for stations this year. There will also be increased opportunities for promotion.
"All of this will ensure that our customers feel safe, fully supported and able to access the right assistance in our stations at all times.
"We encourage the unions to continue working with us on this process and the only way to resolve this dispute is to keep talking about how to improve our stations."