Vietnam is suffering from its worst COVID-19 outbreak yet, state TV reported on Sunday.
Sixteen southern provinces will face restrictions for two weeks, as the country's daily COVID-19 cases hit a new record of over 5,900 infections.
Domestic flights were also suspended to and from the south until next month.
The Health ministry has sent 2,000 ventilators and tens of thousands of its most highly-qualified health workers to hard-hit areas.
Meanwhile, in the capital Hanoi, citizens were told to stay at home.
The city has already stopped indoor dining and closed salons and gyms.
Vietnam has been one of the world's coronavirus success stories due to targeted mass testing, strict contact tracing, and border controls.
But new clusters of infections in recent weeks have triggered concern among health officials.
The country of 98 million has received nearly 9 million doses of COVID-19 vaccines.
Fewer than 300,000 people have been fully vaccinated.