BEIJING (NYTIMES) - When officials in an eastern Chinese city were told to root out "uncivilised behaviour", they were given a powerful tool to carry out their mission: facial recognition software.

Among their top targets? People wearing pyjamas in public.

On Monday (Jan 20), the urban management department of Suzhou, a city of six million people in Anhui province, sparked outrage online when it published surveillance photos taken by street cameras of seven residents wearing pyjamas in public, along with parts of their names, government identification numbers and the locations where their "uncivilised behaviour" had taken place.

City officials quickly apologised, but not before stirring nationwide ire over the use of a state-of-the-art digital tool to stamp out a harmless and relatively common practice - an unusual note of resistance in a country where the instruments of digital totalitarianism have spread largely unchecked.

On social media, the Suzhou department publicly called out, among others, a Ms Dong, a young woman in a plush pink robe, matching pants and orange pointy flats, walking on a street, and a Mr Niu, who was singled out for donning a black and white checkered full pyjama suit in a mall.

"Uncivilised behaviour refers to when people behave and act in ways that violate public order because they lack public morals," read a post on WeChat, a common social messaging app, which has since been deleted.

"Many people think that this is a small problem and not a big deal," the post said. "Others believe public places are truly 'public', where there is no blame, no supervision and no public pressure.

"This has brought about a kind of complacent, undisciplined mindset," it concluded.

The use of facial recognition software by law enforcement authorities remains a hotly debated topic worldwide and has even been banned in some major American cities.

Not so in China. In just a few years, use of the software has become widespread. Police have used it to create a powerful surveillance dragnet and profile racial minorities, giving rise to fears that China represents a future in which governments rule via digital authoritarianism.

The technology is also used to solve more mundane problems. Local authorities use it to catch tissue bandits at public toilets. People use it to board planes and order fried chicken. It is even used on pigs and pandas.

The scope of facial recognition in China, where enthusiasm for new digital tools often outpaces their abilities, is far from clear. Still, many Chinese people have embraced the technology.

But naming and shaming pyjama wearers in Suzhou may have been a step too far. Though China lacks an independent court system or other means to challenge rising powers to track people, an increasing number of citizens are raising privacy concerns, though often focused more on Internet companies than the government.

"Facial recognition technology should be used with caution," a user named Xiu Li De Xiao Wo wrote on Sina Weibo, a popular microblogging platform. "They should really be restricting access."

Some users on the platform said they disagreed with the government's decision to release private information online. Others simply wanted to know what was so wrong with wearing pyjamas in public.

"When celebrities wear pyjamas to an event, they are called fashionable," a user named Cai Shen Jie wrote. "But when ordinary people wear pyjamas to walk around on the streets, they are called uncivilised."

Public pyjama wearing is common in China, particularly among older women, whose outfits tend towards bold colours and floral or cartoon patterns. It is also a popular sartorial practice in the winter in southern China where, unlike in the north, most homes do not have central heating.

The origin of the practice is widely debated, though virtually everybody agrees on one point: Pyjamas are extremely comfortable.

Shanghai especially has been an epicentre of pyjama couture. In 2009, local authorities tried to ban the practice before the World Expo in 2010. Signs reading "Pyjamas don't go out of the door; be a civilised resident for the Expo" were posted around the city while "pyjama policemen" were sent around to patrol neighbourhoods.

Still, the pyjamas-in-public tradition persisted.

Ms Hung Huang, a writer in Beijing writer and proud pyjama-wearing fashion blogger, said the government had no business interfering in the fashion choices of the Chinese public.

"In China, when these things happen, it is when very high technology gets into the hands of very low-level bureaucrats, and by low level I mean low level of intelligence," she said.

"The decision was probably made by somebody who has no understanding of international fashion and of how to use technology to benefit the people rather than to just control them," she added. "This should be an alarm for all Chinese tech developers and Chinese government policymakers."

The Suzhou ban on pyjamas in public is not the first time China has sought to crack down on what it deems uncivilised behaviour. Chinese authorities have imposed fines for public spitting and, more recently, gone after the "Beijing bikini" - or the practice of men rolling up their shirts and baring their bellies in the summer.

Public shaming is a common tactic. In theatres, laser pointers are used to shame audience members who play on their phones during shows. And in Shanghai, facial recognition systems have been installed at some crosswalks to single out jaywalkers.

After the online uproar on Monday, urban management officials in Suzhou quickly took down the original post and issued an apology.

According to the Global Times, a tabloid controlled by the Communist Party, the city had been competing for the title of "National Civilised City", a designation granted by the government, which is why it had banned residents from wearing pyjamas in public.

"We sincerely apologise," the Suzhou department said in a statement posted on WeChat. "The way we released the information and the content of the article were not handled properly."