The atmosphere remained relaxed until darkness at around 8 pm, when the huge police presence, complete with water cannon, became obvious around the access roads into the area around the squatted building known as Rote Flora.
Critics say that such a show of force – with officers drawn from around the country – acts as a provocative challenge to potential rioters.
But Christoph Alhaus, Hamburg’s new mayor and former interior minister with responsibility for such decisions, along with his successor in that office, Heino Vahldieck, said the police would act decisively against any sign of riot.
By 9:30 pm the area around the Rota Flora was tense and the streets were empty of anyone other than people holding beer bottles – and the police.
This year the pubs and restaurants in the immediate area were not only closed but largely barricaded.
But it seems the mood has changed – particularly after rioters this May smashed up local shops rather than the banks and drug stores. Some closed up bars bore signs saying, "Closed against violence."
Some locals were even seen actively trying to prevent the rioting – throwing buckets of water on burning piles of rubbish and pulling apart barricades.
But by 11 pm the erection of a barricade on one street attracted the attention of the police, who were then showered with stones, bottles and some fireworks.
They retaliated with baton charges and water cannons for around two hours, eventually taking control of the streets around Rota Flora and pushing the rioters out of the area.
Several arrests were made, with numbers not yet clear, while at least one police officer and a number of anarchists were injured.
Rioters Clash With Cops After Street Festival
Around 300 left-wing protesters have clashed with police in Hamburg after an all-night street festival in the central Schanze neighbourhood.
Officers responded by turning water canon on the crowds.
Similar riots broke out during last year's street festival when left-wing activists protested against a far-right rally.
Anticipating a repeat of the violent scenes, police had deployed about 2,000 officers in the area.
According to local media reports, several rioters were arrested and two policemen were lightly wounded.
Before the clashes broke out, residents in the neighbourhood had tried to stop the protesters from throwing bottles and rocks.
The annual street party attracts large crowds with its music and food stalls in the central district of the German city and frequently sees clashes between protesters and police.