These cases were reported by a special team of the Ministry of Health in Bac Giang Province, which borders Hanoi, on Tuesday afternoon.

They have yet to be officially confirmed by the ministry as Covid-19 patients, but if they are, it would be the highest number of Covid-19 infections Vietnam has observed over a span of 24 hours.

All the new coronavirus-positive cases had been contained within several zones undergoing social distancing measures.

Tran Nhu Duong, deputy head of the National Institute of Hygiene and Epidemiology, said initial investigations revealed the sources of infection to be industrial parks, factories and worker residences, which often have high population densities.

The health ministry has since instructed Bac Giang to "immediately freeze" all worker residences and strictly apply quarantine measures.

Also on Tuesday, Bac Giang People's Committee requested citizens in Hiep Hoa, Tan Yen, Yen The, Luc Ngan, Son Dong districts and the province's capital Bac Giang Town to remain indoors. About a million people reside in the aforementioned locations, which have been struck with coronavirus outbreaks.

The order however would not be applied for certain cases like those doing official or emergency work.

People would be banned from attending large public gatherings, including for activities like physical exercise or sport. Factories, construction sites and other workplaces must socially distance their employees, including by splitting shifts. Working from home is encouraged.

Bac Giang is currently the worst hit locality in Vietnam by the coronavirus, recording the highest number of cases, at 1,156, since the new wave hit, including 132 on Tuesday.

Most of the province's coronavirus cases are workers at its large-scale industrial parks, which employ thousands.

Factory workers in Bac Giang and its neighbor Bac Ninh now account for around 66 percent of 2,506 confirmed Covid-19 cases in the fourth wave.