(CNN) — They seem like a perfect solution to China's traffic-clogged streets and toxic air: Bikesharing schemes.
They've exploded in popularity in past 12 months, with brightly colored bikes owned by several different companies flooding China's major cities. Residents can rent them via apps on their smartphones.
But some local authorities say the bikes have become a nuisance and one Shanghai district has confiscated almost 5,000 bikes and impounded them in a parking lot. Striking aerial photos of the orange, yellow, blue, green bikes were widely shared by Internet users in China last week.
A man walks past impounded bicycles from the bike-sharing schemes Mobike and Ofo in Shanghai on March 1, 2017.
"Despite making citizens' lives easier, the overwhelming number of shared bikes has paralyzed existing bike parking and management, " a statement from the Huangpu district government said.
"The unregulated parking and riding has caused constant problems and complaints."
A guard who works at the Shanghai parking lot told CNN Monday that traffic police had confiscated the bikes because they had been illegally parked. He added that the bikes were from seven different bikesharing companies.
By Tuesday afternoon, 20% of the bikes had been picked up, a parking manager said.
Shanghai has impounded thousands of brightly coloured bikes placed on city streets by cycle-sharing companies.
Cao Guoxing, a spokesperson for bikeshare operator Mobike said it had reclaimed its bikes "after consulting with the government."
To prevent the problem happening again, Cao said the Mobike app would have a new feature from next week that recommended designated parking spots.
A spokesperson for Ofo, one of the companies whose bikes were confiscated in Shanghai said "some coworkers are following up on the situation" and declined to give further details. The company has one million bikes in operation nationwide.
Bluegogo, another bikesharing company, didn't reply to a CNN request for comment.
This picture taken on February 20, 2017 shows an employee of a parking firm putting bicycles from the bike-sharing schemes into a truck in Shanghai.
That number is expected to jump to a staggering of 500,000 shared bikes by this June, according to Guo Jianrong, secretary general of Shanghai Bicycle Association.
"By then, the market will be saturated," he said.
Until the turn of the century, bikes were the main form of transport in Chinese cities. But in recent years, as Chinese have grown richer, bicycles have been replaced by private cars, motorbikes and better provision of public transport.
This picture taken on January 16, 2017 shows rented bicycles from bike-sharing schemes in Shenzhen.
Bikesharing is hardly new, but what makes it unique in China is that its usually station free -- which means that users can technically leave the bikes anywhere they want.
It's also cheap. It costs just 0.5 to 1 yuan ($0.07-$0.15) for a 30-minute ride.
Shanghai is not the only city in China where bikesharing has had teething problems. More than 500 bikes rented out by bikesharing firms were left piled up in the southern city of Shenzhen in January, the South China Morning Post reported.