The Vietnamese Ministry of Health announced 10 coronavirus cases on Monday, including nine imported infections and one person making an illegal entry.
The imported cases are Vietnamese returnees from Russia, the ministry elaborated.
They landed at Cam Ranh International Airport in Khanh Hoa Province, located in south-central Vietnam, on board flight VN5062 from Russia on Christmas Day.
The nine were sent to centralized quarantine in Khanh Hoa upon entry.
They tested positive for the coronavirus at the Khanh Hoa Center for Disease Control on Sunday.
The remaining patient is a 23-year-old Vietnamese who entered the country illegally from Cambodia on Christmas Eve together with five other people.
He was diagnosed with COVID-19 on Sunday, when he was sent to collective quarantine in District 5, Ho Chi Minh City, the municipal health department said in a report on Monday.
The 23-year-old has been transferred to a makeshift hospital for COVID-19 treatment in the city.
He is in stable health but suffers nasal congestion and chesty coughing.
His place of residence, an apartment building on Su Van Hanh Street in District 5, is now isolated by local authorities.
One of his five companions had earlier been confirmed as a COVID-19 patient on Saturday.
Authorities have found and quarantined all but one of the remaining companions.
Health officials are conducting extensive contact tracing, with scores of their contacts having been isolated.
Vietnam’s patient tally has reached 1,451 as of Monday night, with 1,318 recoveries, including 15 announced tonight, and 35 virus-related deaths, the health ministry said.
The Vietnamese government allows entry to skilled workers, experts, diplomats, and Vietnamese repatriates, who are all subject to mandatory quarantine upon arrival, although it still closes the border to international arrivals to stem coronavirus spread.
Prime Minister Nguyen Xuan Phuc on Monday demanded that local authorities tighten their control of entry along Vietnam's land borders given a rise in the number of illegal migrants.
PM Phuc encouraged every citizen to report any unlawful entry to help the country stem COVID-19 spread.