The Tu Du Hospital in Ho Chi Minh City is treating 16 patients for swine flu, or A/H1N1 influenza, and has quarantined 80 others for observation.
The viral infection is believed to have spread from a woman admitted for a gynecological surgery last Friday.
Doctors at Tu Du, the biggest obstetrics hospital in southern Vietnam, canceled a laparoscopic surgery on a female patient for a gynecological problem after she kept running high fever and complained of muscle pain.
Not long after, many patients, their relatives and medical staff at the hospital reported having the same symptoms.
Tu Du reached out to doctors at the Hospital for Tropical Diseases HCMC to run blood tests, and received confirmation on Saturday morning that 16 people had tested positive with the A/H1N1 type influenza.
The hospital immediately quarantined more than 80 others that it deemed at risk and isolated the Laparoscopy Department for disinfection.
Pregnant women and infants and young children under two are among the groups identified by the World Health Organization (WHO) as being at increased risk for complications arising from swine flu.
The H1N1 virus broke out worldwide in 2009 and was responsible for more than 17,000 deaths.
Some strains of the virus are endemic in humans and cause a small fraction of all seasonal flu while others are endemic in pigs and birds, better known as swine flu and avian flu respectively.
Vietnam has recorded more than 11,000 human infections so far, including first deaths in April 2013.