Travel chaos hit London on Tuesday due to widespread bus service strike because of dispute over pay.

Transport for London (TfL) said the action was "extremely disappointing," warning it will disrupt the life of millions of people all over the British capital.

About 27,000 members of the Unite union at 18 bus companies throughout Greater London walked out for 24 hours as part of a campaign for a single agreement covering pay and conditions.

Only about 44 out of 673 bus routes are expected to operate.

Around 6.5 million passengers have been urged to check the TfL website for the latest updates on bus services.

Reports said some taxi companies raised prices due to an increase in demand for its services on Tuesday morning.

Members of the Unite union complained that with no collective pay deal, there were 80 different pay rates for drivers doing the same job.

The union added that in contrast to Tube drivers, there is no collective pay deal for bus drivers, with wages negotiated on a company-by-company basis.

The drivers say the pay differs from £17,000 to £25,000 a year.

There are more than 80 different pay rates covering drivers doing the same job, leading to differences in hourly rates of over £3, said Unite.

It added the average wage for a London Tube driver was about £40,000 and therefore a "reasonable" wage for a bus driver should be between £28,000 and £30,000.

TfL said the strike will affect services from around 4am on Tuesday and hit night bus services operating tonight into Wednesday morning.

Since there are about 6.5 million bus journeys made every day in London, the stoppage is expected to cause widespread disruption.

A survey of 1,600 bus passengers for Unite showed that two-thirds backed the drivers' campaign.

Wayne King, London regional officer for Unite, said: "London's bus operators have raked in millions in profits while driving down pay and refusing to tackle pay inequality on the capital's buses.”

Unite ridiculed the “huge discrepancies” in salaries within the bus service companies, adding that the drivers were left with no other option except strike.

"As bus company directors enjoy lottery-style salaries, bus drivers doing the same job on the same route are being pitted against one another on different rates of pay,” King said.

"Strike action is the last resort. We've been forced into this position by the operators' refusal to even meet with us. Passengers sitting side by side on the same route expect to pay the same fare, so why shouldn't drivers expect to be paid the same rate?” he added.

However, TfL insists the strike and its impact were unnecessary.

"It is extremely disappointing that Unite has decided to go ahead with this unnecessary disruption, especially given the low turnout for the ballot and low numbers voting for the strike,” Leon Daniels, its managing director of surface transport, said.

"Bus drivers' pay and conditions are a matter for the bus companies and Unite to discuss, as it has been for 20 years, and we continue to urge them to seek a swift and fair resolution for the sake of our passengers,” he added.

A spokesman for Metroline, one of the bus companies involved, said: "We apologise to our passengers for the disruption caused by the strike.

"Only one in five of our drivers voted, with less than one in six voting for strike action. This is an unprecedented low level of support to strike and Unite's decision to pursue industrial action is unnecessary and extremely disappointing.

"Unite is seeking to move to a common rate of pay across all bus companies in London and we have challenged this on the grounds that it would be illegal for us to agree to their demand. We offer attractive and competitive rates of pay to our staff and remain open to discussions to resolve this."

Go-Ahead, another Bus company, said 839 of its drivers out of an eligible workforce of 6,076 voted to strike.

"The very low turnout reflects the fact that the vast majority of staff understand their employer is committed to them. People are at the heart of our business and I therefore urge Unite to call off this action. This is a dispute we cannot resolve,” managing director John Trayner said.

"Strike action is inappropriate and unnecessary. It will ultimately inconvenience the six and a half million people who use the bus network every day and ensure union members lose pay," he added.