Commuters in London are facing travel misery with the entire London Underground network shut down by strikes.
Services were halted on Wednesday night after a walkout by Tube staff over pay and conditions. They will not resume until Friday morning.
The Tube dispute centres on the night services, set to begin in September.
A walkout by First Great Western staff has halved high-speed services between London, the West of England and Wales.
An extra 200 buses are being laid on, as well as additional river services, to help cope with demand in the capital, TfL confirmed.
London Overground, DLR, TfL Rail and tram services are unaffected by the industrial action.
Those able to travel outside peak times are being urged to do so.
London Underground (LU) has warned the strike - the first to close the whole network since 2002 - will cause "big disruption".
On Thursday morning Mike Brown, Managing Director of London Underground, apologised to customers and said: "I am very sorry your journey has been disrupted. This strike is unnecessary."
The strike began at 18:30 BST on Wednesday when members of the Rail, Maritime and Transport (RMT) union, the Transport Salaried Staffs Association (TSSA) and Unite walked out in a 24-hour action.
At 21:30, members of the train drivers' union Aslef began their own 24-hour stoppage.
RMT General Secretary Mick Cash said: "The strike action on London Underground is rock solid across all lines.
"That means an end to the attempt to bulldoze through new working patterns."
The London rush hour was brought forward into Wednesday afternoon as thousands tried to head home early.
But large crowds built up at the busiest Underground stations as people attempted to beat the strike.
Oxford Circus station was intermittently closed and services on the Victoria and Northern lines were temporarily suspended while TfL tried to manage passenger flow ahead of the industrial action.
The Tube strike coincides with a separate, 48-hour walkout by First Great Western staff from 18:30 on Wednesday, causing disruption to rail services between London, the west of England and Wales.
On Monday, members of all four unions rejected a "final" pay offer from LU which included a 2% rise this year and £2,000 for drivers on the weekend night Tube service.
The typical salary for a Tube driver is £50,000 a year, the RMT said, but the unions maintain the new plans would be disruptive to their members' lives.
They claim some employees are concerned they will have to work more overnight shifts and may have to work on their own at some stations.
The disputed weekend night services are set to begin on 12 September on sections of the Central, Jubilee, Northern, Piccadilly and Victoria lines.
Transport Secretary Patrick McLoughlin said the strike was of benefit to no-one.
"We stand shoulder to shoulder with workers, families and commuters who want to go about their lives without disruption. I urge the strikers to accept the good offer that employers have made and get back to work," he said.
Aslef organiser Finn Brennan said the responsibility of the strikes "rests squarely with London Underground management" who "squandered the window of opportunity" to resolve it.
About 20,000 Tube workers are expected to walk out during the course of the strike.
Talks are set to resume on Friday.
Getting about
TfL advice
- Cycle and walk where possible
- Extra bicycles will be available to hire from London's cycle hire scheme in central London
- The DLR, London Overground, bus network, tram and TfL Rail services will operate as normal, however passengers are advised to travel outside of morning and evening peak times on Thursday
- First Great Western staff are striking too - there will be no First Great Western service between Paddington and Greenford for 48 hours from 18:00 BST on Wednesday as a result of separate strike action
- Chiltern Railways services are not stopping at stations between Great Missenden and Marylebone travelling southbound during morning peak time, but a normal service will run after 09:30 BST
- Chiltern Railways services between Aylesbury and London Marylebone via Amersham are also affected by the lack of LU signallers on Wednesday night and Thursday
- Up to 200 extra buses will operate on key routes
- The congestion charge remains in place
Key points of the dispute
- The RMT, TSSA, Unite and Aslef unions say the dispute with London Underground (LU) is about workers' pay and conditions associated with the new Night Tube working
- Union members have voted 9:1 in favour of strike action. Aslef said 81% of its members responded to the ballot
- The unions have rejected a deal including a 2% average pay rise for all Tube employees plus a £2,000 one-off bonus for drivers on the five affected lines - by way of compensating them for night working
- The RMT union says the rejected driver bonus would only have affected 1,000 Tube workers out of a work force of 20,000 and the union believed this was a divide-and-rule tactic
- The unions say they want Tube workers to be fairly compensated for night working which has been linked to poor health
- LU says its pay offer is both "fair and competitive"
- LU says it is hiring 137 more train operators to work on the Night Tube, which would result in existing workers doing "a few extra nights per year within the existing working week"
- LU says no-one was being asked to work more hours than at present
- The offer includes a pay increase in 2016-17 of RPI or 1%, whichever is greater, plus a £500 launch bonus to all staff on the Night Tube lines plus a £2,000 transition bonus for drivers
