Health minister Nguyen Thanh Long said gene sequencing of samples from 12 of 276 confirmed patients, 11 in Hai Duong Province and one in HCMC, a Hai Duong returnee, confirmed it is the U.K. strain.

Officials have yet to identify the source of the transmissions.

The strain is more contagious and has a shorter incubation period, and as a result, in less than a week 276 cases have been recorded, Long said.

"The new virus variant can be transmitted through the air and therefore we need to scrupulously follow regulations on wearing a mask. Those who do not comply must be severely punished."

Quang Ninh and Hai Duong provinces in the north were the first places where cases were detected -- on January 28 -- breaking a streak of nearly two months without local infections in Vietnam.

Long said he has discussed with Quang Ninh authorities the imperative for applying social distancing in Dong Trieu District.

Chi Linh Town in Hai Duong has been locked down since last week and social distancing is in place across the province, now the epicenter of the disease with 207 cases.

Deputy Prime Minister Vu Duc Dam, head of the National Steering Committee for Covid-19 Prevention and Control, said the committee and the health ministry have also discussed with authorities in Hanoi, now with 20 confirmed cases, the need for stronger measures to contain the infection.

"The city is speeding up efforts to identify affected areas and isolate them. The fight against the pandemic there might take longer than we expected."

He has instructed local authorities to limit gatherings, especially in closed, air-conditioned venues.

Vietnamese will celebrate the Lunar New Year, their biggest and longest holiday of the year, next week, and usually people travel back home to celebrate it with their extended families.

Vietnam has had 1,856 Covid cases, 396 still active.

The new wave since last week has also spread to Hai Phong and Bac Ninh, Hoa Binh and Bac Giang provinces in northern Vietnam, Gia Lai Province in the Central Highlands, and HCMC and its neighbor Binh Duong Province.