Dozens of violent small groups devastated downtown Stuttgart.

Police in the German city of Stuttgart said Sunday that 20 people were arrested and four police officers injured after a check for drugs sparked attacks on officers and police vehicles and widespread vandalism of stores in the city center. Police said several hundred people were involved.

The disturbance started as an apparent reaction to a police search for drugs as groups of people partied outside late Saturday and early Sunday in a central park. People then attacked storefronts in a nearby shopping street, according to German public television reports, tearing up paving stones and smashing store windows.

Cellphone video purporting to be of the events circulated widely in social media. Police asked witnesses to upload videos that could provide evidence to assist the investigation.

Stuttgart police said 200 officers responded to the incident and four were injured. They said they were investigating to get a clearer picture of what happened and said they would provide more information later Sunday.