Central districts of Hamburg (St. Pauli, Altona and Sternschanze) have been officially declared as "danger zones", giving police exceptional unlimited powers of search and arrest.
The pretext for this militarization of the city is the popular resistance to the eviction of the occupied social center Rote Flora, which has resulted in huge demonstrations and widespread grassroots activism.
On December 21st, 500 civilians and 120 police agents were injured in the clashes that followed the brutal repression of an initially peaceful demonstration.
Since then popular self-defense groups numbering the hundreds patrol those areas and have attacked police stations and patrols (doubtful, probable police propaganda). The number of political prisoners for this escalation is already of at least 30.
One of the several videos of the December 21st clashes you can find online:
Update: attacks to police stations almost certainly false.
Sare Antifaxista reports (on German sources) that not a single piece of evidence of the existence of such reported attacks exists, in spite of all police stations having many security cameras. It seems to be just a pretext to crush human rights and popular resistance.