Scores of people responded to social media invitations to descend on Platja d'Aro on Tuesday evening and run around pretending to be paparazzi, papers reported.
Participants held tripods and selfie sticks and pretended to be chasing a celebrity. But other people in the streets mistook the objects for guns and fled, blocking traffic and sending restaurant tables flying, media reported.
Eleven people were treated for minor injuries, anxiety attacks and heart palpitations, with at least two hospitalised police said.
Five German women, aged between 20 and 25, were arrested, accused of ivvolvement in the stunt, the force added. They were charged with public order offences and will appear in court later on Wednesday.
Tensions are high after a series of attacks claimed by the Islamic State in France and Germany in recent weeks.
