Chinese authorities are collecting biometric data, including DNA samples, fingerprints and blood types, in the country's western Xinjiang Uighur Autonomous Region, a rights watchdog said.
The Human Rights Watch (HRW) reported that the data was gathered from people between the ages of 12 and 65.
According to the HRW, the data could be used for "surveillance of persons because of ethnicity, religion, opinion or other protected exercise of rights like free speech."
The checks are officially voluntary, but an ethnic Uighur resident said that local cadres forced them to go.
HRW's China director said, "Mandatory data banking of a whole population's biodata, including DNA, is a gross violation of international human rights norms."
Of Xinjiang's 21 million-strong population, some 11 million are Uighurs — a Muslim Turkic ethnic group.
Chinese authorities have been waging a wide-scale security crackdown in Xinjiang which officials say is necessary to curb extremism. Beijing is also reportedly seeking the immediate return of Uighurs studying abroad.
Overseas, Uighurs and human rights groups say the measures have turned Xinjiang into a police state, with widespread arbitrary detentions and invasive surveillance.
