The nine imported cases were quarantined upon their entry in Vietnam.
Five new community transmission cases were detected in Vinh Phuc province near Hanoi. They had close contact with a group of Chinese experts who entered Vietnam on April 9 and completed their quarantine period on April 23 in Yen Bai province but later tested positive with the coronavirus after returning to China.
The two community transmission cases detected in northern Ha Nam province had close contacts with confirmed coronavirus cases associated with a man who returned from Japan and tested positive after completing his two-week compulsory quarantine in Da Nang city.
Since new community transmission cases were detected in late April after more than a month without local infections, Vietnam has tightened COVID-19 prevention measures.
Students in Hanoi from kindergarten to upper secondary school are asked to stay home from Tuesday until further notice, according to the Hanoi Department of Education and Training's document issued on Monday. Students will attend online classes during the school closure, said the document.