The fast-spreading delta variant of the coronavirus has been found in China.
Over the past week, more than 500 cases of COVID-19 have been identified across the country after the first delta cases were found in the port city of Nanjing. On Tuesday, authorities said they had discovered 90 new cases, concentrated in Jiangsu, Henan and Hubei provinces.
The city of Wuhan said it would mass test all 10 million of its residents after discovering eight cases of the virus this week.
Authorities have locked down the hardest-hit neighborhoods, including Zhangjiajie and begun mass testing of all residents. These measures are all part of China's zero tolerance approach to COVID-19 — to contain it at all costs.
Authorities say the delta variant may have come in on the surface of international baggage. From there, infected airport workers passed it on to four travelers who then visited Zhangjiajie, a popular tourist spot known for sharp, vertical mountains that inspired the world in Avatar.
While in Zhangjiajie, they watched a musical performance attended by about 1,000 other people.
From there, performance participants spread the delta variant to at least 18 other provinces — including to the city of Wuhan, where the first strain of novel coronavirus was discovered.
Beijing, China's capital, is being very careful even though it has only 20 COVID-19 cases right now. In a Monday press conference, Beijing health authorities said they are preventing anyone who has been to an area with COVID-19 cases from entering Beijing.
China's immigration authorities also said this week that they are not issuing new passports to their citizens unless there is a pressing need to travel abroad for education or employment.
This story originally appeared on the Morning Edition Live Blog.