The complaints have spiralled into a broader debate on productivity and work-life balance in a country that last year marked the 40th anniversary of adopting free-market reforms.

In neighbouring Japan, a new law came into effect this month capping overtime to 45 hours a month. South Korea last year cut its maximum working hours from 68 hours a week to 52 hours.

The movement in China gained more publicity earlier this month after Katt Gu, a US-trained tech industry lawyer, and Suji Yan, CEO of Shanghai-based digital privacy start-up Dimension, launched the Anti-996 License on Github.

Companies that use the project’s open source software and codes must comply with international labour laws, which prohibit working 996 hours without appropriate compensation.

“This protest might become a turning point for China tech and transform it from a labour-intensive industry to an innovation and creation driven business,” said Yan in an interview.

“Working long hours isn’t a competitive edge for Chinese tech companies. It’s not productive either.”

The South China Morning Post spoke with several software engineers and programmers about their 996 work schedule. All of them said they were not able to fully concentrate for 12 hours. They also asked for anonymity for fear of reprisal by their employers.

“My most productive working hours are from 4pm to 8pm when I can totally focus on coding,” said a Beijing-based engineer for a cloud service provider. “A lot of my time before 4pm is spent on communicating with other colleagues. I can be more focused after they’re gone,” said the engineer.

The engineer also described situations where department heads would walk through the office at night to see who was working late and make key performance indicator (KPI) judgments and personnel decisions based on that.

At Baidu, operator of China’s leading search engine, two engineers separately confirmed that while 996 was not an official requirement by the company, engineers still worked overtime due to peer pressure.

“If you leave at 6pm it is considered leaving early,” said one of the engineers.

In a study by the American Journal of Epidemiology, middle-aged workers who clock upwards of 55 hours a week exhibit a poorer short-term memory and reduced ability to recall words than those who work fewer than 41 hours.

A separate study by UBS found that workers who logged the most hours lived in emerging markets cities.

Based on surveys across 15 different professions in all industry sectors, the top five in 2018 were Mumbai, Hanoi, Mexico City, New Delhi and Bogota – where workers put in between 2,358 and 3,315 hours per year – equal to 45 to 64 hours per week. The Chinese mega cities of Beijing and Shanghai ranked 22nd and 33rd respectively.

However, when it comes to gross average earnings per hour, cities in more developed countries were ahead, with Geneva, Zurich, Luxembourg, Los Angeles and Copenhagen making up the top five.

A senior executive with a Chinese telecommunications firm said in the past the company was able to use “four heads to compete against one” foreign company employee but rising wages in China has meant more attention is being focused on boosting productivity and quality of output.

“We are now in the era of using one head to compete against one head,” said the executive, who declined to be named because he was not authorised to speak to the media.

Beijing-based Bytedance, the company behind the TikTok short video app, has adopted a big week/small week policy for its employees.

That means a six-day week, every second week. Bytedance employees are paid 1.2 times their normal salary if they work on weekends, according to several Bytedance employees. However, Chinese labour law stipulates that employees working weekends should be paid double time.

“No one can work 996 hours indefinitely. People are willing to work long hours only when the company is growing rapidly and there is an extra bonus,” said one of the Bytedance employees.

Another employee at the company admitted that when she has to be in the office for 12 hours every day, there is a natural tendency to spend downtime watching short videos, doing online shopping, and even napping.

Even an eight hour day does not mean being productive the whole time, according to research done in Britain. Vouchercloud, Europe’s biggest mobile voucher app, found that the average UK office worker is only productive for three hours a day.

The report listed the most popular unproductive activities as reading news websites, checking social media, discussing non-work-related topics with colleagues, and job searching.

The anti-996 movement on Github now includes a blacklist of companies that are currently asking employees to work unpaid overtime.

A total of 104 tech companies, including Alibaba, Huawei, Tencent, Baidu, Xiaomi, JD.com and Bytedance were on the blacklist as of Thursday afternoon. The named companies either did not immediately respond or declined to comment on being on the list.

Alibaba is the parent company of Post.

Watch: In 2016, ‘death by overwork’ was on the rise in Japan

Speaking to employees at an internal company meeting on Thursday, Alibaba founder Jack Ma defended 996, saying such a schedule has helped Chinese tech giants like Alibaba and Tencent grow to become what they are today, drawing on his own experience of working long hours in the industry.

The adoption of the 996 work schedule by Chinese tech companies – whether officially or unofficially – was seen as necessary for start-ups to survive during a period of intense growth.

China’s mobile internet population more than doubled from around 300 million in 2010 to 788 million last year, according to the China Internet Network Information Centre (CNNIC), a branch of the country's Ministry of Industry and Information.

“996 was adopted early in the start-up phase to quickly prove the business model and then later to achieve rapid implementation of business strategy,” said Willam Chen, a co-founder of ClearVue Partners, a private equity firm that counts driverless car start-up Pony.ai and online health platform Ping An Good Doctor in its portfolio.

In most cases, company failures are due to having poor strategy in the first place, not the slow implementation of that strategy, Chen said, adding that if the business strategy is not clear or simply wrong, adopting 996 could lead to even greater failure.

“Morale is broken when employees see that their work is meaningless, which makes some 996 companies inefficient,” Chen said.

“Behaviours like watching movies at work [then] start to appear. 996 should probably be stopped when those inefficiency clues start to appear.”

Jixun Foo, managing director at GGV Capital, said he practically worked “24/7” during the merger of video streaming sites Youku and Tudou.

“It’s not about you. It’s about what the market demands. If your peers are working 996 and you want to be ahead of the competition, you need to choose 996 too,” he said.

“The market is like a treadmill. It’s running and running, but when it’s slowing down, you slow down with it.”

Gu, the tech lawyer who co-authored the Anti-996 license, believe companies with a 996 work schedule will eventually go out of business.

“Technology shouldn’t be a labour-intensive industry, it should be a creative industry. Creative people need to take a rest.”