The six-storey archive building in Cologne collapsed into a pile of rubble
Rescue workers are searching for up to four people still missing after a building housing archives collapsed on Tuesday in the German city of Cologne.
Witnesses said there may have been two people inside a car parked outside the archive and another two in a nearby building that subsequently collapsed.
The area must be stabilised before rescue teams can move into the rubble.
Cracks and groaning noises had alerted staff and visitors at the archive, all of whom escaped before it collapsed.
Work was being carried out nearby on a new underground railway, but the company involved said there had been no recent tunnelling.
Gregor Timmer, a spokesman for the city of Cologne, said on Wednesday morning that rescue workers had to assume that between two and four people were still missing underneath the rubble of the archive and two neighbouring buildings.
The buildings to the left and right of the collapse site are severely damaged and are in danger of partly falling down
Gregor Timmer Spokesman for the city of Cologne
"There are reports on two inhabitants of the building next to the archive that collapsed and two people who were inside a car in front of the building at the time of the tragedy," he told the Reuters news agency.
Up to nine people were initially reported missing after the collapse, but several have since contacted city officials, police said.
The archive building dated from the 1970s and contained 65,000 original documents, some of them dating back more than 1,000 years.
There has been no word on the condition of the collection, which includes manuscripts by Communist philosophers Karl Marx and Freidrich Engels and items left to the city by figures such as the Nobel Prize-winning author, Heinrich Boell.
The area must be stabilised before rescue teams can move into the rubble
Mr Timmer said rescuers needed to stabilise the remains of the structures before moving into the rubble to determine whether anyone was trapped inside.
"The buildings to the left and right of the collapse site are severely damaged and are in danger of partly falling down. That is why rescuers are currently unable to step onto the rubble," he added.
On Tuesday evening, concrete was pumped into the ground to firm it up. Two hundred rescue workers are still at the scene.
The six-storey building collapsed at about 1400 local time (1300 GMT), bringing down two other neighbouring buildings.
One witness said the scene resembled a Hollywood movie as cracks slowly spread up the building's facade before it collapsed in a cloud of dust.
It is not yet clear what caused the buildings to collapse, officials said.
Authorities in Cologne have evacuated buildings within a 150m radius around the site, including two schools and a retirement home.
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