At a meeting with the HCMC Steering Committee for Covid-19 Prevention and Control, Dam said the discrepancy was due to illegal entrants using less-traveled paths to cross over borders.

"If they manage to go to events with large gatherings, or bus stations and airports without wearing masks, the risk would be unimaginable," he said.

Dam requested HCMC to severely punish those who do not wear masks in public places, especially as new coronavirus cases have increased by around 34 percent in nearby countries like Cambodia, Thailand and Laos over the past week.

Commenting on the latest two outbreaks in Vietnam, one centered in the central city of Da Nang City in July 2020 and the other in the northern province of Hai Duong in January-February, Dam said the cause for widespread infections in these locations was inadequate prevention measures, especially at hospitals and factories.

Provinces and cities at the south-western border need to ramp up border control measures to prevent illegal entrants, he added.

"After some time without community transmission, people tend to let their guard down, so measures need to be tighter. Illegal entrants and those who don't make medical declarations need to be severely punished," he said.

Nguyen Thanh Phong, chairman of the HCMC People’s Committee, said the southern metropolis had recorded around 108 illegal entrants in the first quarter. He agreed that measures to prevent illegal entrants need to be stepped up, particularly given the city’s trade and commercial activities.

Nguyen Tan Binh, director of the HCMC Department of Health, said the city should strictly punish illegal entrants and make them pay for Covid-19 prevention costs, including quarantine expenses.

As of April 18, HCMC had administered the AstraZeneca Covid-19 vaccine to 9,155 medical workers in the first round. The second vaccination round began on April 19 for around 1,022 medical workers.