The 28-year-old, who has been suspended and faces possible dismissal, could be charged with "spreading dangerous infectious diseases in human", the police said at a press conference on Thursday.

It carries a jail term of up to 12 years.

This is the first time that flouting Covid-19 prevention regulations is being treated as a crime, they said, pointing out that in the past people were let off with fines.

The flight attendant had returned to Vietnam from Japan on November 14 and was quarantined for four days at a facility managed by Vietnam Airlines in HCMC's Tan Binh District.

After two tests showed he was negative for the coronavirus, he was let go but told to isolate himself at home.

But he came into contact with his mother and two friends, including an English language teacher who stayed with him for a few days.

On November 29, 15 days after he returned from Japan, he tested positive for the virus, and the next day the teacher did too. The latter had meanwhile spread the virus to a nephew and a student of his.

The flight attendant told authorities he had left home on Bach Dang Street in Tan Binh District at noon on November 21 to eat on Le Van Sy Street in Phu Nhuan District.

He then visited Hutech University in Binh Thanh District on November 22.

The teacher’s diagnosis on Monday ended Vietnam’s 88-day streak of no local transmission.

Under Covid-19 prevention protocols, flight crews must isolate themselves on returning to Vietnam. But the flight attendant went to another quarantine area and contracted the virus from another crew member who had returned from Romania.

Two Vietnam Airlines isolation facilities in HCMC have since been shut down, forcing 61 employees to be quarantined in two hotels. The carrier on Wednesday also issued a public apology.

Following the incident, the Ministry of Transport on Tuesday said airlines whose crews flout Covid-19 quarantine rules and transmit the infection would not be allowed to operate international flights.

Hanoi and HCMC also proposed scrapping preferential quarantine regulations for aviation staff, meaning flight crew members returning from abroad should instead be sent to centralized quarantine facilities for the usual 14-day isolation. Currently, flight attendants are allowed short-term quarantine to ensure staff availability for flights.

Vietnam has had 1,358 Covid-19 cases so far, 119 still active. Thirty five have succumbed to the disease, many of them elderly patients with underlying conditions like diabetes or kidney failure.