Collapsed building traps 3 in GermanyStory Highlights
Rescuers say three trapped under collapsed building in Cologne
Number of people missing reduced after six people contacted officials
Media: Firefighters are using dogs to help search the rubble at city's archive
Reporter: Archive building evacuated, those trapped were in gambling hall
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(CNN) -- Rescuers in Germany have reduced the number of people they are searching for in a building collapse from nine to three after six people who had been reported missing contacted the fire department.
Rescuers are searching for people trapped under the building in Cologne, Germany.
1 of 2 The six saw their names on television and called the fire department to say they were safe, a fire department spokesman explained.
Hundreds of rescue workers continued to search the ruins of the collapsed building in Cologne, Germany Tuesday for the other three people who may be trapped beneath the rubble.
The city's historic archive collapsed, damaging two other buildings, said Carlo Schlender, a reporter for German TV station RTL, a CNN affiliate.
Firefighters were using dogs to help search the rubble, and police said heavy-lifting equipment was on the way, CNN's Ben Brumfield reported from the scene.
Rescuers do not know if anyone is alive in the rubble, he said. iReport.com: See photos of the rescue scene
As many as 100 emergency vehicles were on the scene, he added.
The collapse of the main building tore the facade off a neighboring structure, revealing the rooms inside, photos from the scene showed,
Rescue efforts are ongoing and are expected to last until at least midnight local time (2300 GMT), a fire department spokesman told CNN. The spokesman did not identify himself.
Police are evacuating all the buildings in a 150-meter (yard) radius around the scene of the incident, including two schools and a retirement home housing 76 people, Brumfield said. There will be no classes at the school Wednesday, he added.
The building did not collapse quickly, Schlender said, giving people the chance to flee.
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There were "a lot of noises before (the collapse). Most of the people could hear that something was wrong and escaped from the scene," he told CNN International's "iDesk" program.
The fire department confirmed that everyone in the archive managed to escape before the collapse of the building, but some people working and living in buildings next door were not able to escape.
The city is building a new subway line directly under the buildings that collapsed, Susanne Motter at the Cologne tourism bureau told CNN. It is not clear if the underground construction played a role in the incident.
But Gudrun Meyer, a spokeswoman at the Cologne Transportation Department, denied building works were taking place below the collapsed structure.
"This construction is not happening directly under the building, nor am I aware of any contraction which might have caused this," she told RTL.
The main building which collapsed is the Historic Archive of the city of Cologne, which houses documents up to 1,000 years old.
The building itself was an unremarkable 20th-century structure, but the archives it contained were very valuable, said Brumfield, who has done research in the building.
Andreas Gress, a CNN iReporter who lives near the building and passes it every day on the way to work, said he saw nothing unusual Tuesday morning at 8 a.m.
"People were working like every day," he said.