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German police say more than a dozen police officers were hurt during the violence, in south-west Germany.
Video clips on Twitter show people vandalizing shops in the city center and hurling big stones and other objects at police vehicles.
Stuttgart police say the violence began after police checked a drug incident.
The situation escalated after a 17-year-old was questioned for an alleged drug offense, the city's police vice-president Thomas Berger told reporters.
A group of between 100 and 200 people responded by throwing stones and bottles at the police on the central Schlossplatz, a large square.
This then grew, he said, to between 400 and 500 people attacking police. Many of the rioters were said to be hooded and masked.