However, whether the new strain’s virulence was greater than that of previous variants has yet to be confirmed, Nguyen Thanh Long, acting Minister of Health, said at a meeting with the National Steering Committee on Covid-19 Fight and Prevention Monday morning.

Vietnam has recorded five strains among its previously confirmed cases, making this the sixth strain, he said.

"The new strain came from outside of Vietnam, but we don't know from which country. The health ministry has submitted the new strain's data to a world gene bank for comparison," Long said.

Central Da Nang City has confirmed three Covid-19 community transmissions over the weekend: two men, aged 57 and 61, and a 71-year-old woman. Another community transmission, a 17-year-old boy, was recorded in the nearby Quang Ngai Province, though it was confirmed he had visited Da Nang on July 14.

All four cases had either been at or in contact with someone in Da Nang Hospital, Da Nang Hospital C and the Orthopedic and Physical Rehabilitation Hospital of Da Nang. All three hospitals are located on the same plot in Hai Chau District, and have since been put under lockdown.

On Monday morning, Prime Minister Nguyen Xuan Phuc announced Da Nang would enter a period of social distancing for at least 14 days starting Tuesday to curb the spread of the novel coronavirus. The government’s Directive 19 on social distancing requires citizens to maintain a distance of at least one meter from each other and prohibits gatherings of more than 20 persons in public, except in offices, schools and hospitals.

Residents are encouraged to stay at home. Festivals, religious ceremonies, sports and other events that gather a large number of people are banned. "Non-essential" businesses including entertainment facilities, beauty salons, massage and karaoke parlors, and bars are closed.

Several localities have requested arrivals from Da Nang to report to authorities and get tested for Covid-19 as well.

Vietnam has recorded 420 Covid-19 cases so far, with 55 remaining active. The first community transmission in 100 days was confirmed on Saturday to be a 57-year-old man in Da Nang, breaking Vietnam's 99-day streak of no community transmission.