People in China are now required to have their faces scanned when registering new mobile phone services, as the authorities seek to verify the identities of the country's hundreds of millions of internet users.
The regulation, announced in September, was due to come into effect Sunday.
The government says it wants to “protect the legitimate rights and interest of citizens in cyberspace”.
China already uses facial recognition technology to survey its population.
It is a world leader in such technologies but its intensifying use across the country in recent years has sparked debate.
China seeks to root out fake news and deepfakes with new online content rules
Chinese regulators have announced new rules governing video and audio content online, including a ban on the publishing and distribution of “fake news” created with technologies such as artificial intelligence and virtual reality.
Any use of AI or virtual reality also needs to be clearly marked in a prominent manner and failure to follow the rules could be considered a criminal offense, the Cyberspace Administration of China (CAC) said on its website.