The police in China are collecting blood samples from men and boys from across the country to build a genetic map of its roughly 700 million males, giving the authorities a powerful new tool for their emerging high-tech surveillance state.

They have swept across the country since late 2017 to collect enough samples to build a vast DNA database, according to a new study published on Wednesday by the Australian Strategic Policy Institute, a research organization, based on documents also reviewed by The New York Times. With this database, the authorities would be able to track down a man’s male relatives using only that man’s blood, saliva or other genetic material.

An American company, Thermo Fisher, is helping: The Massachusetts company has sold testing kits to the Chinese police tailored to their specifications. American lawmakers have criticized Thermo Fisher for selling equipment to the Chinese authorities, but the company has defended its business.

The project is a major escalation of China’s efforts to use genetics to control its people, which had been focused on tracking ethnic minorities and other, more targeted groups. It would add to a growing, sophisticated surveillance net that the police are deploying across the country, one that increasingly includes advanced cameras, facial recognition systems and artificial intelligence.