The new case is a 42-year-old man who lives in Thanh Hoa Town of the north-central province.
He had come into contact with a group of Chinese male experts who tested positive with the coronavirus after returning to China later.
The experts had arrived in Vietnam early April and had been quarantined at a hotel from April 9-23 in northern Yen Bai Province, during which they tested negative thrice.
After completing their quarantine, the men began working at the Trung Bac A Company in the province and continued to have their health monitored for 14 days at another hotel by local medical staff. But they had breached the self-quarantine regulations, left their hotel and visited many localities in northern Vietnam. After they had returned to China, four of them were confirmed positive for the virus by Chinese authorities.
With the latest case in Thanh Hoa, Vietnam has recorded 121 Covid-19 community transmission cases since April 27. Before then, it had been clean for over a month.
Cases have been recorded in 15 localities: three cities of Hanoi, Da Nang, HCMC and the provinces of Ha Nam, Vinh Phuc, Hung Yen, Quang Nam, Dong Nai, Hai Duong, Yen Bai, Thai Binh, Bac Ninh, Lang Son Quang Ngai and Thanh Hoa.
Since the beginning of the pandemic, Vietnam has registered 1,691 locally-transmitted cases aside from 1,400 imported cases.