BERLIN (AFP) - Hundreds of people ran riot in Germany's Stuttgart city centre in the early hours of Sunday (June 21), throwing stones and bottles at police and plundering stores after smashing shop windows.

"Police are currently securing leads and are interrogating more than 20 people who have been provisionally arrested," authorities in the southwestern city said.

More than a dozen police officers were hurt in the clashes, it added.

"I sharply condemn this brutal outbreak of violence, these acts against people and things are criminal action that must be forcefully prosecuted and condemned," Baden-Wuerttemberg state premier Winfried Kretschmann said.

Interior minister for the region Thomas Strobl said the riots were of "an unprecedented nature".

Sascha Binder, a leading local MP of the Social Democratic Party, had earlier described the violence as "civil war-like scenes".

Tensions built up shortly after midnight over police checks on drug taking by people who had gathered close to the city's biggest square, the Schlossplatz.

Clashes then broke out, as the groups went on the rampage, using sticks or poles to smash windows of police vehicles parked in the area.

Police estimated that around 500 people were involved in the riot, which also left shops along the neighbouring Koenigstrasse, a key shopping thoroughfare, looted.

Police called in reinforcements, and managed to quell the violence only several hours later.

Videos posted on Twitter showed people breaking shop windows, leaving goods strewn on the streets.

A jewellery store was completely emptied and a mobile phone shop wrecked, according to regional broadcaster SWR.

Smaller scale clashes had broken out downtown last week between police and groups of young people.