RIO DE JANEIRO, Brazil (AFP) — Gangs of young thieves set off panic and chaos over the weekend as they raided Rio’s famous Copacabana and Ipanema beaches, less than a year before the city hosts the Olympics.

Local television showed groups of adolescents grabbing cell phones, backpacks and other valuables as they swept through the beaches, sending sun-seeking tourists and residents fleeing in shock — some in tears.

One scene captured on video shows a youth throwing sand into the face of a police officer. He fled only after the officer drew his gun.

Brazen incidents such as these are not uncommon on Rio’s beaches in the summer. The youths are rarely caught since they quickly disappear into the crowds, loot in hand.

In an unusual development Saturday evening, however, the incidents spread beyond the beaches into the well-off Humaita and Botafogo neighbourhoods.

More than 20 children and adolescents who got off a bus in plain sight of police proceeded to steal from both passers-by and stores, causing shopkeepers to lower their metal shutters. A fruit vendor was shot in the leg.

In response to the robberies, Copacabana residents who call themselves “vigilantes” and organise via social media decided to take matters into their own hands and attacked a bus returning to the suburbs Sunday, smashing its windows and berating passengers who jumped out of the windows in fright.

The police intervened but the “vigilantes” still managed to beat some of the youths on the bus, with footage of the violence posted on social media.

The wave of incidents follow a recent court decision that bans the police from searching buses headed to the beach and preventively detaining youths if they have not committed any crimes.

Human rights activists say just being young and black was enough to land a person in preventive detention.

In the wake of the incidents, Jose Mariano Beltrame, the secretary of security in Rio state, charged that police can no longer “act preventively.”

Rio is to host the 2016 Olympics next August.

Last month, the head of an International Olympic Committee fact-finding mission said the city would stage great Games — as long as it sorts out “millions” of details first.