The stunt, believed to be staged by German tourists, took place around 10pm in an area of packed restaurants.
The group burst onto the scene brandishing what people believed were guns and screaming. Tourists on the busy waterfront promenade thought they were witnessing a terrorist attack and ran for cover, causing a stampede.
In fact, it later emerged the group were carrying tripods and were posing as paparazzi to stage a supposed celebrity sighting.
At least eleven people were injured and one man suffered a heart attack in the ensuing panic.
Five tourists, all German, were arrested and will appear in court on Wednesday morning on charges of causing public disorder.
Witnesses took to social media to describe how diners in restaurants dived under tables to take cover.
“My parents were there in Platja d'Aro. They were eating in a restaurant and threw themselves to the floor taking cover under tables,” said Quique Gallemi.
Mis padres estan en Platja d'Aro. Estaban cenando en un restaurante y se han tirado al suelo y se han cubierto con las mesas...— Quique Gallemí (@QuiqueGallemi) August 2, 2016
The police were quick to explain it as a false alarm and urge people to remain calm.
There've been relevant incidents in Platja d'Aro streets caused by flash mob that derived in stampede, it's a FALSE ALARM— Platja d'Aro Policia (@platjaropolicia) August 2, 2016