“Accordingly, people in red areas must shelter in place and one person of every household there will be tested three times per week,” a statement from city authorities said, adding that in other zones people would be tested every five to seven days.
Barricades on Monday separated red zones from other areas, photographs posted on social media and media outlets showed.
Hanoi authorities expect up to 1.5 million test samples to be collected in the next week. The government is eager to keep the outbreak from reaching the intensity seen in Ho Chi Minh City.
In the southern business hub, people have been encouraged to test themselves using antigen COVID-19 kits after health services were overwhelmed.
Hanoi has been reporting on average 50 cases daily and has recorded over 4,000 cases since the pandemic began, official data showed.
Although the numbers are still low, authorities are wary after the Delta variant has helped drive up infections across the country to over 524,000 cases.
One-third of Hanoi’s eight million residents have been fully vaccinated and on Sunday the health ministry called on the capital and Ho Chi Minh City to vaccinate all adult residents with at least one dose by Sep 15.
Vietnam has one of the lowest coronavirus vaccination rates in the region, with only 3.3 per cent of its 98 million people fully vaccinated, and 15.4 per cent with one shot.