A second strike is planned for 12 September
Bus drivers in London have begun a 24-hour strike, which will affect 80 routes, in a row over pay.
About 2,500 employees of First began the strike on Friday, a move expected to mainly affect bus routes in the east and west of the city.
Members of the union Unite want a standard £30,000 rate of pay for drivers across the bus network.
A union spokesman said the walkout had been "solid" but First said a number of routes were running.
BBC London's travel reporter Steve Phillips said the strike had not had much of an affect on the roads and rail.
But he said: "There were huge queues at bus stops and the few buses which are running are packed, with people reporting passengers having to stand on the top deck."
Unite said there were "just four or five workers driving" and services had been badly affected by the solid turnout.
But a spokesman for First said some bus drivers had reported for work and 14 routes were running services out of the company's nine London bus depots.
Union members decided to go on strike after rejecting a 4% pay increase deal on Wednesday.
A First spokesman said its pay offer was "reasonable" and the action would affect 14% of London's bus network.
Unite said pay disparity between London's 18 different bus operators could be as much as £6,000. Sick pay, pensions and holiday arrangements also differed, it added.
It wants all of London's 28,000 bus drivers to be paid £30,000 a year, based on a 38-hour week.
The industrial action includes drivers who work for First Capital East and Centrewest London Buses, which operate under First.
Unite members plan a further 48-hour walkout on 12 September.
Transport for London said it was trying to keep the disruption from the strike to a minimum and urged people to check before they travel and find alternative means of transport.
The routes affected in east London are 58, 67, 91, 150, 165, 179, 191, 193, 212, 215, 231, 236, 252, 259, 299, 308, 309, 323, 339, 341, 357, 365, 385, 389, 399, 476, 488, 498, D6, D7, D8, RV1, W6, W10, W11, W12.
The routes affected in west London are 9 (heritage service only), 10, 18, 23, 28, 31, 79, 83, 92, 95, 105, 187, 207, 223, 224, 226, 228, 245, 282, 295, 328, 331, 414, 427, 487, 607, A10, E1, E3, E5, E7, E9, E10, PR2, U1, U2, U3, U4, U5, U10.