Bus drivers in London are taking part in a 24-hour strike over pay differences between the capital's 18 bus companies.
Members of the Unite union walked out at 00.00 GMT (5 February), leaving travel disruption for commuters.
Transport for London has said around 47% of its bus routes were running, but warned there would be disruption to services across the city and to night buses early on Friday morning.
Today's strike is the first of three as part of a long-running campaign for a single agreement covering pay, terms and conditions. The next are scheduled for 13 and 16 February.
Unite has said there is no collective pay deal between drivers, meaning that there are 80 different pay rates for drivers doing the same job as wages were negotiated depending on the company. The union said hourly rates can vary by more than £3.
Pete Kavanagh, London regional secretary of Unite, told BBC News: "We've got a two-tier workforce in which people coming into the industry in recent years never get to the top rate of pay. We've literally got hundreds of rates of pay and this has got to stop."
TfL has said the strike is "totally unnecessary" and that it will cause "significant" disruption. TfL's director of buses has claimed "levelling up" pay would cost around £100m a year, resulting in a "cut to bus services, an increase in fares, or both."
The bus companies likely to be affected are: Abellio (Abellio London and Abellio West London); Arriva (Arriva North and Arriva South); CT Plus (Hackney Community Transport); Go Ahead (Blue Triangle, Docklands, London General, London Central, Metrobus); London Sovereign; London United; Metroline (Metroline and Metroline West); Stagecoach (East London Bus & Coach Company, Selkent); and Tower Transit.
Bus services on Friday should operate as normal.
Unite has posted a graphic on Twitter explaining the bus strike:
Which bus services are running?
66 - Romford Station to Leytonstone bus station
142 - Watford Junction to Brent Cross Shopping Centre
160 - Catford to Sidcup Station
258 - Watford Junction to South Harrow Station
268 - Golders Green Station to Finchley Road
288 - Queensbury to Broadfields Estate
298 - Arnos Grove to Potters Bar
303 - Edgware Station to Colindale
305 - Edgware Station to Kingsbury Circle
340 - Edgware Station to Harrow Bus Station
346 - Upminster Station to Upminster Park Estate
370 - Romford to Lakeside Shopping Centre
375 - Romford Station to Passingford Bridge
404 - Coulsdon to Caterham-on-the-Hill
406 - Kingston to Epsom
411 - Kingston to West Molsey
418 - Kingston to Epsom
428 - Erith to Bluewater Shopping Centre
463 - Coulsdon South Station to Pollards Hill
465 - Kingston to Dorking
467 - Hook to Epsom
470 - Colliers Wood Station to Epsom
492 - Sidcup Station to Bluewater Shopping Centre
499 - Gallows Corner to Heath Park Estate
626 - Finchley Central Station to Potters Bar
628 - Kingsbury to Southgate Station
631 - Golders Green Station to Henrietta Barnett School
641 - West Molesey to Teddington School
642 - West Hendon Broadway/Edgware Station to London Academy
653 - Muswell Hill Broadway to Kingsbury
683 - Friern Barnet to Kingsbury
688 - Southgate Station to Kingsbury
B12 - Erith to Joydens Wood
B13 - Bexleyheath Shopping Centre to New Eltham Station
B15 - Bexleyheath Shopping Centre to Horn Park
E10 - Northolt to Ealing Broadway Station
H2 - Golders Green Station circular (via Hampstead Garden Suburb)
H3 - Golders Green Station to East Finchley, Hilltop
H18 - Harrow Bus Station circular (via Pinner & Wealdstone)
H19 - Harrow Bus Station circular (via Wealdstone & Pinner)
K5 - Ham to Morden Station
S1 - Banstead to Lavender Fields
S3 - Sutton Hospital to Malden Manor Station
X26 - West Croydon to Heathrow Airport
How long does it take to walk between tube stations?
A walking map - shared on social media with the hashtag #WalkLondon - is a good alternative for those wanting to avoid public transport.
How can you use Oyster cards, travel cards and tickets?
TfL has said the following ticket acceptance arrangements will apply during today's strike.
Bus & Tram Pass season ticket, 11-15 Zip Oyster photocard or 16+ Zip Oyster photocard with free bus & tram travel will be accepted on Tube, DLR and London Overground services on reasonable routes only. Passengers should show their Oyster card to a member of staff and ask to be let through the gates. Customers should not touch in or out as they will be charged a pay as you go, which will not be refunded.
Bus & Tram Pass season tickets will also be accepted on MBNA Thames Clippers RB1 River Bus service between 06:00-10:00 and 16:00-19:00.
Bus & Tram Pass season tickets will not be accepted on National Rail services or the Emirates Air Line.
One Day Bus & Tram Passes will not be accepted on any alternative services and refunds will not be given.
Pay as you go users will be charged the appropriate fare for the journey for the service(s) and zones used and these fares will not be refunded.