At the height of China’s coronavirus outbreak, officials made quick use of the fancy tracking devices in everybody’s pockets — their smartphones — to identify and isolate people who might be spreading the illness.

Months later, China’s official statistics suggest that the worst of the epidemic has passed there, but the government’s monitoring apps are hardly fading into obsolescence. Instead, they are tiptoeing toward becoming a permanent fixture of everyday life, one with potential to be used in troubling and invasive ways.

While the technology has doubtless helped many workers and employers get back to their lives, it has also prompted concern in China, where people are increasingly protective of their digital privacy. Companies and government agencies in China have a mixed record on keeping personal information safe from hacks and leaks. The authorities have also taken an expansive view of using high-tech surveillance tools in the name of public well-being.

The government’s virus-tracking software has been collecting information, including location data, on people in hundreds of cities across China. But the authorities have set few limits on how that data can be used. And now, officials in some places are loading their apps with new features, hoping the software will live on as more than just an emergency measure.

Zhou Jiangyong, the Communist Party secretary of the eastern tech hub of Hangzhou, said this month that the city’s app should be an “intimate health guardian” for residents, one that is used often and “loved so much that you cannot bear to part with it,” according to an official announcement.

Governments worldwide are trying to balance public health and personal privacy as they pull out the stops to protect their people from the virus. In China, however, the worry is not just about potential snooping.

The country’s leaders have long sought to harness vast troves of digital information to govern their sprawling, sometimes unruly nation more efficiently. But when computer systems have so much authority over people’s lives, software bugs and inaccurate data can have big real-world consequences. It is also far from clear that citizens are comfortable with their government knowing so much about them, even when the aim is efficiency and convenience.

“Epidemic prevention and control needs the support of big data technology, but this does not mean agencies and individuals can randomly collect citizens’ information by borrowing the name of prevention and control,” Li Sihui, a researcher at Huazhong University of Science and Technology in Wuhan, wrote in a recent commentary.

People in China sign up for the virus-tracking system by submitting their personal information, recent travel and health status in one of a swath of apps. The software uses this and other data to assign a color code — green, yellow or red — that indicates whether the holder is an infection risk. Workers posted outside subways, offices and malls stop anyone without a green code from entering.

The authorities have never explained in detail how the system decides the color of someone’s code, which has caused bewilderment among people who have received yellow or red ones without understanding why. The New York Times reported in March that one widely used piece of health code software collected location data and appeared to send it to the police, though it is unclear how the information was used.

In Hangzhou, where the system was pioneered, officials are exploring expanding the health code to rank citizens with a “personal health index,” according to a post last week on an official social media account. It is not clear how the ranking would be used. But a graphic in the post shows users receiving a 0-to-100 score based on how much they sleep, how many steps they take, how much they smoke and drink and other unspecified metrics.

The backlash was swift. “Doesn’t this brazenly violate privacy to surveil and discriminate against unhealthy people?” Wang Xin, a novelist, wrote on the social platform Weibo, where he has 2.5 million followers.

“I know that in this age of big data, it’s so easy for those who control data to check and use personal information in a matter of minutes,” another author, Shen Jiake, wrote. But Hangzhou’s plan “crosses a line,” he said.

This month, Robin Li, the head of the Chinese search giant Baidu, proposed at a meeting of China’s top political advisory body that the government create a mechanism for deleting personal information collected during the pandemic.

If the authorities have specific reason to hold onto health code data after the threat has passed, then they should make those reasons clear and obtain users’ consent, said Lei Ruipeng, a professor of bioethics at Huazhong University of Science and Technology, in an April interview with the state-run outlet Health News.

So far, no such mechanism has materialized.

China’s health codes first appeared in February, the joint products of local officials and tech companies, including the internet giant Tencent and Ant Financial, a sister company of the e-commerce titan Alibaba. Within weeks, codes were popping up across the country.

As armies of guards, workers and volunteers began to be posted throughout cities to check people’s codes, the apps became essential to daily life. They have even become an accidental tool for fighting crime.

The Hangzhou police announced this month that they had apprehended a man who had been on the run after committing a murder 24 years ago. Without a health code, he couldn’t work or find a place to stay, the police said. After wandering the streets for days, he turned himself in.

Chinese cities are now trying different ways of keeping residents glued to their virus apps. Shanghai wants its app to become a digital assistant for accessing local services of all kinds, not just medical ones. In the inland city of Xining, the software unlocks coupons to local stores as a way to boost the economy.

In Hangzhou, the authorities in April began linking the city’s app to citizens’ medical records. This has enabled residents to schedule hospital visits using the app. A document from the city government also outlines situations in which people’s codes could be scanned to receive a readout of their overall health.

When seeing a doctor, for instance. Or when evaluating workers for jobs, like being a driver, that require physical fitness. Even when monitoring crowds at large gatherings.

Such readily accessible information could enable discrimination, however. Insurers could raise rates for people with red or yellow codes. Employers could deny jobs or promotions.

China’s internet regulator in February issued guidelines barring personal information collected to fight the epidemic from being used for other purposes. But it is not clear whether the same stricture would bind apps, like Hangzhou’s, that were created to combat the virus but then morphed into a more general tool.

Neither the internet regulator nor Hangzhou health officials responded to requests for comment.

In one county in Zhejiang Province, where Hangzhou is the capital, officials are extending the health code concept beyond public health, a possible sign of where this experiment in digitized social control might lead.

Recently, Communist Party officers in Tiantai County, near the city of Taizhou, were inspired to develop a separate tool they call the “honesty health code,” the local deputy director of operations, Qiu Yinwei, said by telephone.

The code represents party members’ degree of uprightness and diligence in carrying out party work.

“It’s about whether your party spirit is healthy, not whether your body is healthy,” said Xu Yicou, the party secretary of the village of Shitangxu.

Like the original health codes, the honesty codes come in green, yellow or red. For now, they are not generated by software on individuals’ phones. Instead, officials generate them based on their records about party members.

After the codes are printed out on paper, they can be scanned with a phone app to bring up more information. Party members with red codes face investigation and discipline, according to Zhejiang Daily, a state-run newspaper.

The paper this month told the story of Xu Xujiao, the party secretary of Youyi New Village. The local seniors’ association had misused public funds, the paper said, and as punishment, Mr. Xu’s honesty code was changed from green to yellow.

In response, he “promptly changed his thinking, corrected his attitude and devoted himself to his work,” the paper reported.

Before long, his code was green again.

Wang Yiwei contributed research.