Yu Guofu, a partner with Beijing Shengfeng Law firm, says taxi-hailing apps make it easier to call taxis and do not breach any laws, regulations or policies. However, questions over the legality of car-hailing apps are murky.

Chinese law provides for an administrative penalty for unlicensed ride services, Yu says. But most of these laws and regulations apply to an old-style planned economy and are ill-suited to developing rules on a passenger transport market in a modern society, he says.

Yu says the number of taxis in Beijing has failed to rise as the population has risen, so supply cannot meet demand. That breach has been filled by the cars one can call on apps, a method that also counteracts the price gouging that customers and potential customers can encounter with so-called illegal black taxis, he says.

"If something like this promotes social progress, growth of the industry and is in the public interest, we need to legalize it rather than sticking to old ways of thinking."

Chen Yanyan, vice-president of the School of Metropolitan Transport at Beijing University of Technology, says: "Big cities rely on public transport such as subway and buses, but they are not meeting people's expectations. There is a demand for car hailing, but it really ought to supplement other ways of getting about.

"The car-hailing apps market does need to be regulated. They are giving taxis the incentive to offer better service, but there are legitimate concerns about unfair competition and safety."

At the moment, car-hailing app companies, in a fierce battle to gain market share, are splashing out huge sums of money that are in effect subsidies, she says. In addition, private car owners are not professional drivers, and the service life of private cars and taxis are different.

Chen suggests public transport be improved by being more flexible in the services that are offered. One example is small, comfortable buses with air-conditioning and free WiFi for anyone willing to pay a premium for the service.

Yu, the lawyer, advises passengers using car-hailing apps to keep documentation of their trips, including receipts, as a legal safeguard.