HANOI (REUTERS) - Vietnam was back on high alert for the novel coronavirus on Saturday (July 25) after medical officials in the central city of Danang detected what appears to be the first local Covid-19 case in the Southeast Asian country for three months.

Thanks to strict quarantine measures and an aggressive and widespread testing programme, Vietnam has kept its virus total to an impressively low 415 cases, and had reported no locally transmitted infections for 100 days.

But on Friday, Vietnam's health ministry said in a statement that a 57-year-old man from Danang, a popular tourist hot spot, had tested positive three times for the virus, prompting the isolation of 50 people he came in contact with.

One hundred and three people connected to the patient were tested for the virus but all returned negative results, the statement said.

The health ministry has not officially confirmed the case as Covid-19, which comes at a time when Vietnam was about to resume international commercial flights and as domestic tourism is surging.

It did not say how the man contracted the virus, but said he had not left Danang for nearly a month. He was initially diagnosed with pneumonia.

Late on Friday, authorities in Hanoi reinstated a recommendation to wear masks in public places as Vietnam's benchmark VN Index closed down 3.22 per cent.

The country's ban on international commercial flights is still in place, but foreign experts and skilled workers have been able to enter Vietnam throughout the pandemic provided they undergo mandatory centralised quarantine.

Of the nearly 150 cases reported over the past three months, all were imported and the people quarantined on arrival. Earlier this week, Vietnam said it would repatriate around 130 Vietnamese citizens infected with the virus from Equatorial Guinea.

In March, Danang reported six local cases of the coronavirus as the US aircraft carrier Theodore Roosevelt conducted a port visit to the city.