It was an ordinary mid-July day in Qinhuangdao, a coastal city in Hebei province. Yang Sheng was on his way to work and happened to see an electrical power box covered in thick rust.

He stopped, took a picture with his cellphone and uploaded it to a digital management platform using an app called Citywide Management Inspectors. He wrote a brief description of the problem and gave the location of the box.

The whole process took about two minutes.

Over the next several days, the city's urban management office contacted all the telecommunication companies operating in the area but couldn't find the owner of the box. So they went in person, visiting nearby companies. At last, they found that it was owned by a nearby shopping center.

On July 21, five days after his posting, Yang got a call informing him that he might want to check the app again to see a picture of a new power box, which had been installed to replace the rusty one.

Yang is far from alone. The digital platform handles a massive number of tips from members of the public every day.

"We began to promote the app in late April and have turned more than 8,000 volunteers into our eyes. The group is still expanding rapidly," said Li Yaobin, director of the Qinhuangdao urban management office. "They are our fans and intend to closely watch the city's performance. Just imagine how powerful the group will be if the figure of active users reaches 10,000."

Li said Beijing has its so-called Chaoyang qunzhong and Xicheng aunties－residents who provide crucial information on public security. They've risen to prominence on Chinese social media.

"Now, Qinhuangdao has its own citywide crowd of inspectors," Li said.

Chen Jianfu, director of the digital city management supervision and command center, said there are strict deadlines for handling certain cases. Illegal street stalls, for instance, should be dealt with-in three hours; broken pavement should be fixed within five working days.

In 2015, the city－famous for its shoreline and as a summer resort for Chinese leaders since the 1950s－vowed to turn itself into one of the cleanest in the country.

Now, with an urban population of about 1.4 million, the city has mapped a digital grid－an overlay in which every road is assigned to four people of various levels－from municipal leaders to sanitation workers, Chen said. Once a problem is identified, the people in charge of fixing it can be found by simply clicking the map.

An early step was the ability to track all sanitation vehicles to assess daily performance.

All security cameras in the city have been linked to the system and are continuously monitored.

Xie Xiaobing, deputy director of the urban management office, said that in the past, during the rainy season, the city was nervous about flooding, especially in underpasses, and sent staff members to keep an eye on high-risk places.

Now, cameras do the watching, and water levels are monitored automatically. If it reaches a warning line, the area will be blocked off.

"We can do many other things on the platform. It is a war map of our daily work," Xie said.

The efforts have paid off. Last year, Shanhaiguan district got the highest score in Hebei province as a clean city.

"I visit Qinhuangdao about three times a year and have witnessed impressive changes, from sanitation to management," said Wang Xu, 66, a tourist from Beijing. "Now more of my friends intend to spend the summer here."