They were among 23 people attending a party at the restaurant on Ngo Quyen Street in Hai Duong Town, the capital of the namesake northern province, on July 31.

After the Ministry of Health confirmed on August 12 that a 63-year-old man working as a security guard there was infected with the coronavirus, local health authorities called on everyone visiting the restaurant between July 10 and August 11 to make medical declarations.

Only four of the 23 at the party did so by last Friday.

It took the police two days of searching to find the identities and addresses of the remaining 19.

They fined 13 of them but let off the rest since they are under the age of 16. All have been quarantined at home.

Besides the guard, three more employees and a customer who visited the restaurant have also contracted Covid-19.

Hai Duong Town was locked down and began a 15-day social distancing campaign from Friday that requires people to stay at home, maintain a distance of at least two meters from each other in public and avoid public gatherings of more than two except at offices, schools and hospitals.

Authorities have told people not to leave town except with permission. All non-essential businesses like restaurants, bars, karaoke and beauty parlors, and hairdressers are closed.

Since July 25, when local transmission returned after three months, 488 cases have been reported in 15 cities and provinces, including Hanoi and HCMC.

Vietnam’s Covid-19 count is now 964, including 484 active cases. Twenty four people have died so far.