The Berlin police searched apartments in the partially occupied house "Rigaer 94" in Berlin-Friedrichshain on Wednesday morning.
A police spokeswoman said a good 300 emergency services were involved.
"We are executing a judicial search warrant here in the house." It was issued at the request of the owner.
The personal details of the residents should be determined, said the spokeswoman.
Berlin - "Some of the emergency services are in the house and already in the apartments." The street in front of the house is blocked.
On Twitter, the police asked residents to stay in their apartments and to be quiet.
The street in Friedrichshain is best known for the partially occupied house at number 94. The building complex is a symbol of the left-wing radical scene.
There have been repeated violent clashes with the police there.
The project has long been a bone of contention in politics.
dpa