As decided by the Mekong Delta province, Tan An Town and the four districts of Duc Hoa, Ben Luc, Can Duoc and Can Giuoc will follow Directive 15, which requires suspension of social events, bans gatherings of 20 people or more in one place and of 10 people or more outside workplaces, schools and hospitals, requesting a minimum distance of two meters between people in public.
The move came as the province recorded eight Covid-19 cases in the past five days.
Pham Tan Hoa, its deputy chairman, said the five localities subjected to the social distancing rule are home to a total population of around one million.
Lying right next to Ho Chi Minh City (HCMC), they are densely populated and home to many industrial complexes, he said.
The province has also suspended all types of passenger transport services to and from those districts, only allowing buses carrying workers to factories to operate.
In other districts across the province, restaurants and coffee shops are only allowed to serve takeaways.
Administrative offices in the province have stopped receiving physical documents, calling for these to be sent digitally or via the post office.
Aside from setting up Covid-19 checkpoints along its gateways, Long An has requested all people entering the province from infected areas in HCMC between May 20 and June 1 to be tested for the new coronavirus and isolate themselves at home.
Those arriving from areas not hit by Covid-19 in HCMC have to sign agreements stating they will avoid going out as much as possible.
Of the eight cases in Long An, five are linked to the ongoing cluster that emerged from a Christian congregation in HCMC a week ago.
The other three cases are a father and two sons in Can Duoc District, whose source of transmission is still under investigation. The youngest son, a 22-year-old student at HCMC's Huflit University, was the first to develop Covid-19 symptoms after returning home on May 23.
HCMC imposed Directive 15 across the entire city starting Monday.
Vietnam has recorded as many as 4,597 local infections in 37 of its 63 cities and provinces since the new wave hit in late April.