Barricades were erected around the attendant's house while authorities told people in the neighborhood to wear masks and refrain from getting near the area.
Three people in the attendant's family - her mother, husband and child - have been put in home quarantine.
The flight attendant, 30, tested positive with the Covid-19 virus once, Hanoi Chairman Nguyen Duc Chung said at a meeting Friday. Further tests are needed to officially put her in the infection list.
Vietnam Airlines says the attendant was on flight VN54 from London to Hanoi which landed at 5 a.m. on March 9.
She took time off from March 9 to 11. On March 10, she started coughing and had high fever. On March 11 morning, she took a taxi to a medical center for aviation employees for a health check-up, before going to the National Hospital of Tropical Diseases 2 in the afternoon the same day. She tested positive for the Covid-19 virus on March 12.
The flight she served carried 221 passengers and crew members. The plane has been disinfected.
Hanoi authorities have tracked down 94 foreigners on the flight, most staying in Hanoi's Hoan Kiem District, Hanoi authorities found.
Vietnam has officially confirmed 44 Covid-19 cases so far, 16 having been cured and discharged from hospitals. As of Thurday night, the country has quarantined around 268 suspected Covid-19 cases in multiple hospitals.
The Covid-19 outbreak has thus far spread to 127 countries and territories around the world, killing close to 5,000.