Hamburg police spokesman Rais Kunz said an annual neighbourhood festival that drew 8,000 people with food booths and live music deteriorated late on Saturday when a small group of revellers started throwing stones through windows.

Police said the violence escalated as others built barricades in the streets and set fire to a car, a telephone booth and a portable toilet.

Police said they used water cannons and that rioters responded by throwing bottles and stones that injured 11 officers.

Mr Kunz said it took 950 officers to subdue the violence and that 38 people were detained for questioning and 19 taken into custody.