The arrests were made after managers of convenience stores on Le Loi Street in District 1 complained with local police, saying a gang of youth armed with stones and some sharp objects broke into their stores several times, taking both money and goods.

Investigation found the suspects had attacked employees at local stores for robberies in at least three occassions this month.

On July 9, they came to one shop at 1:30 a.m., used a glass bottle to threaten an employee and took VND2.1 million ($90). Three days later, they returned and took VND1.8 million.

On Wednesday night, the gang, armed with flick-knifes, carried out another robbery but it is not known how much they robbed.

The three detained suspects, Pham Nguyen Ngoc Tien, 17, Tran Van Thang, 16, and Vo Nguyen Thanh Phuc, 13, said they took money to buy drugs and play online games.

Last year, police in Saigon also detained 11 people, most of them teenagers, for carrying out dozens of after-midnight robberies at 24-hour convenience stores in the downtown area between April and June.

The number of convenience stores in Vietnam has increased by 21 percent year-on-year to 1,819 as of last year, a survey from market research firm Q&Me found. Most of them are based in Hanoi and Ho Chi Minh City.

Among these, many are open 24 hours, with just one or two employees working in the late hours, protected by no guards.