Mainland China has reported its first case of the highly transmissible Omicron variant in the northern city of Tianjin, posing what could be the biggest threat to date to the country’s zero-COVID strategy, writes The Guardian.

The Chinese authorities reported on Monday that the Omicron case was detected on 9 December from an overseas returnee, who showed no symptoms on arrival. The patient is being quarantined and treated in a designated hospital.

At the same time, the eastern province of Zhejiang has been battling a rise in new infections of the Delta variant in recent weeks.