China is accused of locking 1 million people of the Muslim Uighur ethnic minority in detention centers or re-education camps in the country.

According to a new Human Rights Watch report, a Uighur man was detained for changing his watch to two hours behind Beijing time.

The man had reportedly changed his clock to Urumqi time, which follows the natural daylight schedule in the western region in Xinjiang.

China has just one official time zone, but is so big the natural daylight schedules differ across the country.

Changing clocks to "Urumqi time" is seen as a form of resistance against the Chinese government.

China detained a man of the Uighur ethnic minority because he set his watch to a different time from Beijing, Human Rights Watch has said in a new report.

The unnamed man was arrested for being a terrorist suspect and sent to a detention center in Xinjiang, western China, the nonprofit reported, citing a former detainee identified by the pseudonym Nur. The date of the arrest and detention was not clear.

The activist group's source, who was identified by the pseudonym Nur, said: "I know of a guy ... who was taken away for having set his watch to Urumqi time — they say that's what makes him suspicious for terrorism."

China justifies its surveillance and crackdown in Xinjiang as preventing terrorism, and has repeatedly accused militant Uighurs of starting terrorist attacks across the country since at least the mid-1990s.

Former detainees have detailed both physical and psychological torture in China's political camps. Recent inmates also described being forced to sing patriotic hymns in Chinese, and deprived of food if they did not comply, The New York Times reported.

Uighur men pray before a meal in Turpan, Xinjiang, in September 2016. Kevin Frayer/Getty

Urumqi time, or Xinjiang time, is an unofficial time zone set two hours behind Beijing's.

China has one official time zone for the entire country — China Standard Time (CST) — which follows Beijing hours. But because the country is so big, Beijing is actually two hours ahead of the natural daylight schedule in Xinjiang, which is in the west.

Mao Zedong, the founder of modern China, merged all of the country's time zones into one to enhance "national unity."

Setting clocks to "Urumqi time" is therefore seen as a form of resistance against the Chinese Communist Party.

Xinjiang and Beijing are on opposite sides of the country, but are mandated to follow the same time zone. Google Maps; Business Insider

Chinese authorities have used various excuses to justify detaining Uighurs in recent months.

Earlier this week, authorities in Xinjiang arrested four Uighur journalists for being "two-faced," a term used to mean paying lip service to the Chinese Communist Party but privately criticizing its policies, Radio Free Asia reported.

The Chinese government has denied that internment camps exist, but have acknowledged a program of "resettlement" for people it refers to as extremists.