A group of 15 middle school pupils have been detained in Beijing on suspicion of carrying out a series of muggings in the Sanlitun area, a popular commercial district in the capital's downtown.

Police said the gang had operated late at night and targeted multiple victims in the district, which is known for its bars and shopping centers.

The youngest of the suspects is 13 and all study at a nearby middle school, officers said.

One of the suspects, surnamed Zhai, said they had spent the money from the robberies in bars and karaoke venues nearby.

Police used security footage to track down the gang members, who are accused of threatening their victims with knives and other weapons.

They allegedly worked in small groups, wearing masks and changing outfits frequently.

It is not known how many people fell victim to the gang, but one surnamed Jin was recently interviewed by the Beijing Morning Post.

"I was just walking along when two teenagers ran into me and asked me for money because they said they were hurt," he was quoted as saying.

"I wanted to ignore them but they suddenly took out a knife and told me to ‘behave' — I was too frightened to fight back."

Jin said the teens took all the cash he had on him, in addition to taking money from his electronic wallet and forcing him to withdraw more cash from an ATM. In total, they stole more than 2,100 yuan ($300), he said.

The gang was busted after police noticed a suspect that resembled one of the robbers from the surveillance footage during a nightly patrol. He later admitted that he was scouting for new victims and led officers to his alleged accomplices.