"Suddenly there was a rumbling, as if a train were going past," witness Alfred Hoovestaedt, who works nearby, told n-tv television. "Then the noise got louder and louder, and we heard vibration. Then, in seconds, the whole area was covered in a haze."
Fire department spokesman Daniel Leupold said staff and visitors were able to get out of the archive shortly before the collapse, but two construction workers inside were missing.
Work was being carried out on a new subway line under the street on which the building stood, but the cause of the collapse not yet clear, Leupold said. About 180 firefighters rushed to the scene.
"I am not aware of any work at the moment that might have caused this," said Gudrun Meyer, a spokeswoman for the subway company.
The rubble spilled out up to 70 yards (meters) away, police spokesman Wolfgang Baldes said. The roof of the subway construction site collapsed, but officials said they did not believe anyone was trapped in there.
Florian Hacke, who lives two buildings away, said he ran out of his house after he heard a creaking noise and cracks opened up in his ceiling.
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