Vietnam announced the second locally-transmitted case of COVID-19 in two days on Sunday morning, with the source of infection unknown and contact tracing underway.
The patient comes from Da Nang, a beach city in central Vietnam, the National Steering Committee for COVID-19 Prevention and Control said.
The new case is a 61-year-old man living in Thanh Binh Ward, Hai Chau District.
His conclusive test returned positive for the virus on Saturday evening.
He is on mechanical ventilation in the intensive care unit of Da Nang Hospital.
The source of infection is now unknown and Da Nang authorities are conducting extensive contact tracing.
On Saturday, another 57-year-old patient from the city was confirmed to catch the new coronavirus from an unkown source after undergoing five tests, all coming back positive.
Vietnam had gone 99 days without a single local infection before this case, now subject to outside-the-body life support, was recorded.
The Ministry of Health has sent three special task forces to help Da Nang fight the virus insurgence.
Vietnam has recorded 418 coronavirus infections as of Sunday morning, with 276 imported cases.
A total of 365 have beaten the virus while zero deaths have been documented in the country.
Fifty-four patients are being treated for COVID-19, eight having tested negative for the novel coronavirus at least once.
At the time of writing, the Southeast Asian country is quarantining 11,187 people who had close contact with confirmed patients or made an entry from outbreak-hit regions, according to the health ministry.
Vietnam is still closing its borders to foreigners but foreign experts and skilled workers are allowed to enter the country, subject to government approval and compulsory quarantine on arrival.
The government has also sent planes to other countries to repatriate Vietnamese citizens, also quarantined upon landing.
Police in Da Nang have arrested three people on charges of working for a ring to unlawfully take Chinese across the border to Vietnam, according to local media.