HANOI -- Officials in Son Loi, near the Vietnamese capital, said on Wednesday that they had sealed off the entire district for 20 days in response to a flare-up of the new coronavirus.

The district, which has a population of about 10,000, is located about 50 km from Hanoi.

The lockdown of a commune, as Vietnam's subprovincial districts are called, is possibly the first such widespread quarantine imposed outside China, where the epidemic began. Vietnam shares a border of about 1,200 km with China.

"Residents will not be allowed to leave the affected area for the next 20 days," starting Thursday, according to the province of Vinh Phuc, where Son Loi is located.

The move comes after reports that a 3-month-old girl had contracted the coronavirus from her grandmother. The girl was the 10th case in the province of COVID-19, as the infection is known, the government online portal VGP News said. The case suggests human-to-human transmission is taking place in the district.

More than 90 other people were under close health monitoring at Son Loi as of Wednesday.

The lockdown also follows an announcement by Japanese auto parts maker Nihon Plast on Jan. 31 that three employees at its local subsidiary were infected with the virus. The employees work at a factory near Son Loi and had returned from Wuhan, the epicenter of the outbreak, after receiving training at a facility the company operates in the Chinese city.

Vinh Phuc Province has a cluster of Japanese automakers operating there, including Toyota Motor and Honda Motor. Nihon Plast is building a factory in the province to supply auto components.

"Everything is under control," Le Duy Thanh, vice chairman of the Vinh Phuc provincial People's Committee, said Thursday, although he acknowledged the number of infections is rising, according to VGP News.

The secretary of the provincial party committee approved a proposal to postpone reopening schools at all levels until Feb. 23. The province also set up a field hospital with 300 beds to quarantine and treat coronavirus patients. The central government has also ordered provincial hospitals to send doctors and nurses to the affected district.