Shoppers walking along Dublin’s Henry Street close to where the riot took place last week. Photo: Mark Condren

Innocent shoppers were attacked and workers were threatened at knifepoint after rival gangs of up to 250 youths clashed during a riot arranged on social media.

Several people were injured during the shocking incidents of violence on Mary Street, spilling onto Henry Street, on St Stephen's Day.

The terrifying incident occurred on one of the busiest shopping days of the year and as many as five people are believed to have been assaulted.

At one point, shops locked their doors to protect customers inside.

Two large rival groups of teenagers, mainly from Blanchardstown and Tallaght, arranged the confrontation on Facebook and a number of individual melees among the youths were filmed and shown on the Snapchat social media app.

Running

The incident worsened shortly after 7pm as thousands of shoppers descended on the city centre to take advantage of the post-Christmas sales.

"At one point about 90 to 100 youths came running up the street together. They were all shouting at the same time and filming themselves with their phones," a Mary Street sales assistant said.

"Later, the staff locked the doors of the shop for the safety of customers inside. The customers didn't want to leave the shop because they didn't feel safe," she added.

An assistant manageress of another shop said: "We heard it was all arranged on Facebook. A crowd of kids meeting up for a fight. I was very worried about leaving the shop to go home.

"I'm black and look younger than I am and I was afraid the teenagers would think I was a member of one of the gangs and attack me. The store manager walked me to my bus stop."

Despite hundreds of youths being involved in the disturbance, as few as five gardai were on hand to deal with the situation and directed the teenagers to leave the area.

One teenager was arrested for public order-related offences.

"This is an ongoing problem, especially on bank holidays when there is no school," a Mary Street shop manager said.

"They meet up on Mary Street and often begin to fight. We've had to pull down our shutters to protect our customers and to keep them out of the shop. There aren't enough gardai around."

Group

Another shop worker said around 100 of the teenagers ran through the street to watch a fight which had broken out. Later, a big group ran in the other direction when a garda car arrived.

"I'd like to tell them to stop their stupid behaviour," he said.

Officers at Store Street Garda Station are continuing to investigate the orgy of violence as a public order incident.

"This group have been causing absolute havoc in the city over the last few weeks.

"They've been threatening security staff with knives but what happened on St Stephen's Day was far worse though," said a source.

Completely innocent shoppers were punched and assaulted as they walked past some of the gang members.

"I saw three garda cars and an ambulance on the street around 7pm," a local security man said.

"These gangs arrive mainly at weekends and fight among themselves. They don't appear to be using drink or drugs but they make a mess."