The total of cases stays at 268 with no deaths and 70 people now in hospital.
Also on Friday 21 patients were discharged after recovering, 17 in Hanoi, three in the southern province of Tra Vinh and one in the northern province of Ninh Binh.
Thirty nine people are currently being treated in Hanoi, 10 in Ninh Binh, nine in Ho Chi Minh City and the rest in several other provinces.
Of the 70 still in hospital, 13 have tested negative once and four others, twice.
The latest Covid-19 case, diagnosed on Thursday morning, is a 16-year-old Hmong girl from the mountainous province of Ha Giang near China.
"Patient 268" is from a remote village in Dong Van District, and the first case detected in the northern province.
The government decided on Wednesday that the social distancing campaign will continue until April 22 in Hanoi, Ho Chi Minh City and 10 other localities deemed to be at high risk of Covid-19 spread.
The global death toll in the pandemic has exceeded 147,000.