Gardaí are believed to have foiled a planned raid on a sports store in Cork City.
They were alerted as dozens of young people began to gather on Patrick Street at around 5.30pm yesterday evening.
Most were dressed in black, and some were carrying balaclavas.
Gardaí say they deployed additional resources to the area after being made aware of the potential for an incident.
The crowd dispersed without any arrests being made.
An investigation is underway and gardaí continued to patrol the area overnight.
Local Labour Councillor John Maher said the incident was "chilling and sobering".
In a Facebook post, he said: “When traders should be looking forward to the festive shopping season get underway they now have to contend with supposed mass raids?
"I commend gardaí for dealing with this but those identified need to face serious penalties and mother involved must be brought to book.”
He also said he will be writing to the Justice Minister and Garda Commissioner to request that special branch officers are drafted into the city.