BEIJING (NYTIMES) - Stepping off a stylish, compact, orange-and-silver bicycle on the sidewalk outside her Beijing office, Cao Dachui kicked down its metal stand and locked the back wheel. Her less than a kilometre ride from a nearby subway station cost just 14 US cents (20 Singapore cents), and she could leave the bike anywhere.

"It's so very convenient," Cao, 27, said as buses and cars roared by, disgorging the stink of gasoline exhaust. Walking to the advertising agency would have taken twice as long. "Life has really gotten easier," she said. Her friend Ma Zheng, 23, who was parking his own shared bike, nodded.

Beijing was once a city of bikes, the capital of a country known as the Bicycle Kingdom for the millions of two-wheelers that dominated urban transport in a state-planned economy where cars were reserved for official business and the politically powerful.

Decades of remarkable economic growth, beginning in the 1990s, led to a huge influx of cars in cities like Beijing, where owning one became not just a marker of reaching the middle class but also practically a prerequisite for marriage. As the economy roared, autos pushed bikes off the roads, creating heavy pollution and miserable traffic.

Now, Beijing may be returning to its roots - with a modern twist. Thanks to about two dozen technology startups, brightly coloured shared bikes have flooded Beijing since last year, dotting a normally drab cityscape with flashes of bumblebee yellow, kingfisher blue and tangerine.

Beijing commuters have long endured packed buses and airport-style security checks at subways, so many Chinese like Cao are embracing the shared bikes for the flexibility and freedom they offer. Commuters pick up the bikes and then ride and drop them off anywhere they like, locking the back wheel, with no need to find a stand or retether them, in contrast to city bike programs in Paris or New York.

Urban obstruction is nothing new here. Scooters whiz down sidewalks and cars often park randomly, even on crosswalks, giving daily life in Beijing the feeling of a hectic video game. But the bikes - strewn around the city like bright candies - have taken Beijing's chaos to another level, and drivers are particularly upset.

"In the last few months, the bikes have been going crazy. They're like monsters occupying the city," said Huang Linwei, 29, a designer who drives to work in Beijing every day from Tongzhou, an eastern suburb. "More than once I've found it difficult to park my car because the bikes are parked all over the place!"

Others fear for their livelihood. Xu Jianmin, 56, an electric rickshaw driver, said he had made less money transporting commuters since the tens of thousands of bikes began appearing this winter.

"I know our business is kind of a gray zone, that we are not registered with the government, and of course nobody cares if we're affected," Xu said. "But I have to make money."

"I probably would like the bikes, too, if I had another job," he added.

There have also been highly publicized instances of misuse and vandalism. In February, police detained two nurses at a military hospital in Beijing for five days after they locked bikes with chains to stop others from using them.

Angela Cai, a spokeswoman for Ofo, a market leader in bike-sharing in cities across China, said the company was working to address the dumping of bikes in public places. Workers wearing heavy blue coats can now be spotted on side roads in Beijing's Chaoyang district, picking up discarded Ofos.

This month, the municipal government said it would issue parking, management and maintenance regulations for the bikes by June, and it expected the companies to cooperate.

Riding the bikes requires only a few taps on a smartphone. Customers download one of the startups' apps, electronically transfer a deposit and then pay per ride by using a bike's individual code. Bikes that rely on mobile technology feel right at home in a place like Beijing, where even elderly people are often early adapters of technology.

Some companies offer booking services and even GPS to enable riders to find the nearest pair of wheels. But it does not always work as well as it sounds - some riders may not find the bike immediately if it's on a different floor of a high-rise mall, for example.

Costing as little as 7 cents per half-hour and designed to take people the last leg from public transport to their places of work or entertainment, the bikes have the potential to transform urban living and even shape people's decisions about where to live and work. Those are vital issues in this sprawl of about 20 million people, many of whom spend hours a day commuting.

"Having a bike like this might allow me to choose, say, to live a bit further out, or take another job in a place that isn't as easy to get to," said Cao, the employee at the advertising agency.

Analysts in China say there are three factors behind the sudden surge: a lot of cash looking for a home, a good idea and government support.

Since March 2015, two industry leaders - Mobike and Ofo - have attracted about US$750 million in private investment from China and overseas, the bulk of it in recent months, according to Ofo and Caixin, a financial magazine.

But easy money is only part of the story, according to Wang Chenxi of Analysys, a Chinese data and analysis firm. "Behind this is the push of capital, but shared bikes are a good product," Wang said in an interview via WeChat, a messaging app.

"Capital needs an outlet, and just at that moment, shared bikes came along."

Cai, the Ofo spokeswoman, said the company thought that as the city's population grew, and traffic jams got worse, "shared bikes could solve the 'last mile' problem in an environmentally friendly way."

Another important reason for the speed and scale of the investment in the bike-sharing startups is government support, said Lin Chen, a professor at the China Europe International Business School, which is based in Shanghai. "Capital only goes quickly to industries that the government supports," she said.

The bikes have become so popular so quickly that they have also led to questions in Chinese media of an industry bubble and predictions of a battle for market share among the different startups, like what happened among ride-hailing companies in China. Uber China ultimately sold itself to its fiercest rival there, Didi Chuxing.

A recent headline on the Chinese portal sohu.com asked: "Are the recently extremely popular shared bikes a bubble, or the next Didi?"

Among frequent users of the bikes, they provoke a tangible sense of enthusiasm - even glee.

One recent afternoon, Feng Yuqin, 70, used her smartphone to unlock a bike parked on a sidewalk near Cao's office. She said she used to ride either her own pedal bike or her electric bike to the park to exercise, but the bikes had been stolen a few times.

"With these, there's no loss," she said. "It makes me really happy!"