An easier ride, but for some only (3)

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Although the apps already have legions of fans in both cities, some people have criticized the fact most of the software requires users to "bid" for taxis, effectively offering drivers a guaranteed tip starting at 5 yuan (80 cents).

"I won't use these apps," said Li Fangwei in Shanghai, adding that 5 yuan is already more than a third of the city's standard flag-drop charge.

"Also, I can easily get a cab if it's a good fare, such as to the airport, without an app," he added.

Other people have taken to the Web to brand the apps "auctions in disguise" and complain that they merely increase the fierce competition for taxis and push up fares.

YYzhaoche - literally, shake to hail - is among the apps with a tip function. Launched in February 2012, it already has more than 100,000 users in Beijing and is expected to be available in Shanghai after the Lunar New Year.

However, unlike other taxi apps that are free to use and require a cash gratuity be given to the driver, any tips paid digitally to YYzhaoche are pocketed by the software company not the drivers.

Wang Weijian, who created the software, defended the function. He said it is a sign of the market-driven economy, and predicted that all taxi apps will eventually charge for the service when they become popular enough.

"Taxi drivers don't want to go to places where they know they will be trapped in a traffic jam, they don't want to waste petrol going in circles searching for passengers either," he said. "At the same time, passengers don't want there to be no cabs on a rainy night."