HANOI (BLOOMBERG) - Vietnam is keeping people in quarantine centres longer than the 14-day period in its latest step to prevent the spread of the coronavirus amid the emergence of cases being traced to overseas travellers.

Provinces were instructed by the Health Ministry to "temporarily keep" in quarantine until further notice people who have completed the 14-day isolation, according to a post on the government website.

Three patients in Vinh Phuc were found to be carrying a virus variant first detected in India, the health ministry said.

The authorities are scrutinising cases, including that of an Indian national who checked into a hospital in Hanoi on May 3 and tested positive for Covid-19 on Tuesday (May 4).

This was after he had completed the required 14-day quarantine when he arrived in Vietnam on April 17. He was isolated in a hotel in the coastal city of Haiphong and tested negative twice after ending quarantine.

The Hanoi government has placed the apartment building that is home to about 1,500 people - including the Indian national - under temporary lockdown, according to the city's health department.

The authorities are also keeping a close watch on the case of a hotel staff member in Danang whose transmission is still unknown, Tuoi Tre newspaper reported.

Vietnam, which has among the lowest number of infections in South-east Asia, has ordered movement restrictions after domestic Covid-19 cases flared up for the first time in a month.

The nation is lagging behind peers in the region on vaccination, according to Bloomberg's vaccine tracker.

Hanoi has shut schools, tourism sites and sidewalk eateries while Ho Chi Minh City shuttered cinemas, spas and gaming venues and suspended conferences. As at the morning of May 4, Vietnam had a total of 2,985 cases and 35 deaths.