"The fourth wave of Covid-19 in Vietnam included infections in industrial zones, multiple sources of infections and the presence of various coronavirus variants. It will spread very fast and it will be very difficult to control," the health minister said.

The World Health Organization said on Saturday its Virus Evolution Working Group was working with officials in Vietnam to confirm the possible new coronavirus variant after four people were confirmed to be infected with a suspected new strain.

"We have not yet made an assessment of the virus variant reported in Vietnam. We expect that more variants will continue to be detected as the virus circulates and evolves and as sequencing capacities are enhanced worldwide," said WHO's technical lead for Covid-19 Maria Van Kerkhove in a statement.

"From what we understand, the variant they detected is the B.1.617.2 variant possibly with an additional mutation, however we will provide more information as soon as we receive it."

The B.1.617.2 variant was first detected in India, where officials have said it and other variants have driven the country's spike in Covid-19 cases.

British health officials earlier this month upgraded B.1.617.2 to a variant of concern due to its rapid spread in the UK.

New restrictions as cases rise

The new measures, in place for two weeks from Monday, include the closure of non-essential services, such as shops and restaurants, and the suspension of religious activities.

Public gatherings of more than 10 people are also banned, and the city is considering halving that number, according to Reuters.

The outbreak has spread to more than 30 of Vietnam's 63 cities and provinces, including the capital Hanoi, which has shut restaurants and banned public gatherings.

In a country of more than 96 million people, fewer than 30,000 -- 0.03% -- have been vaccinated, according to JHU data.

Vietnam has so far received 2.9 million doses and aims to secure 150 million this year, Reuters reported.