One person caught the coronavirus. China locked down 200,000 of their neighbors.

The extreme response underlines China’s hypervigilance as Beijing prepares to host the Winter Olympics in February amid new local cases of the omicron variant.

The city of Dongxing, which borders Vietnam in China’s southern Guangxi province, on Wednesday ordered all households to quarantine at home until further notice after a resident tested positive during a routine screening, according to state broadcaster CCTV. Schools, public transportation and most businesses, except for supermarkets and pharmacies, were temporarily shuttered as authorities launched a campaign to test everyone in the city.

Customs processing in the city, the entry point for a million tons of goods annually from Vietnam, was also halted while the Chinese Embassy in Hanoi asked Chinese citizens in Vietnam not to return by land.

Authorities in Xi’an in Shaanxi province locked down the city of 13 million, allowing only one person per household to go outside every other day to buy supplies — measures reminiscent of the unprecedented lockdown of the city of Wuhan in early 2020.