Beijing: Tianjin, a major Chinese port city near the capital of Beijing, began testing the mass of 14 million residents on Sunday after a group of 20 children and adults tested positive for Covid-19, including at least two with Omicron variants.
Those infected include 15 students aged 8 to 13 years, a staff member in the center after school and four parents.
City testing must be completed for two days.
China has improved the Zero Tolerance Covid-19 strategy in the run-up of the winter Olympics, which opened February 4 in Beijing.
Chinese capital is 115 kilometers (70 miles) northwest Tianjin and connected with a high-speed train link which takes less than an hour.
Millions of people were locked up in their homes in Xi’an and Yuzhou, two other cities far away but had a larger outbreak.
The city of Zhengzhou, the provincial capital of 70 kilometers (40 miles) North Yuzhou, also conducted mass testing and closing schools starting on Monday.
The first two cases confirmed in Tianjin were a 10-year-old girl and a 29-year-old woman who worked in the school center after school.
Both are infected by the Omicron variant.
In further testing from close contact, the other 18 was tested positive and 767 was tested negatively on Saturday night.