Nguyen Thi Chi, 27, on Sunday said the missing daughters aged 3 and 7, were two of four siblings.
Every day, Chi would drive her four children on the motorbike from District 7 to the Nguyen Hue walking street to sell candies, from 2 p.m. to 7 p.m.
On April 3, she let her 10-year-old daughter take care of her 9-month-old baby and sell candies on Dong Khoi Street, while she took care of the other two siblings and selling candies on the other side of the street.
By 7 p.m., she asked a beverage vendor to watch over her two children, before walking for about 100 m to meet a person to pay back a sum of money.
"I borrowed some money. Every day, before I stop selling candies at around 7 p.m., I would walk over to that person to pay them the money, and then I would take my children home," she said, adding that when she returned about five minutes later, the children were gone.
She asked her 10-year-old daughter if she saw her siblings, but she did not know where they went. She then reported what happened to authorities.
She said her two previous husbands neither stayed with her nor gave her child support after she gave birth.
When her children went missing, she contacted her two husbands, who said they did not have the children.
Her own parents in central Vietnam are sick and elderly, and so cannot take care of the children.
Le Nguyen Viet Nam, deputy head of the Ben Nghe Ward, said authorities have deployed personnel to look for the children.
By Sunday noon, there had been reports saying the two children went with a stranger, but camera footage at the scene did not capture such an incident.
Nguyen Hue walking street, spanning over 670 m, has been operational for nine years and is often crowded on the weekends.