“I now consider that almost irresponsible,” he told public broadcaster ARD, adding that Cologne officials would have to weigh the risks of underground works in the heavily populated centre. “It's not the only building that has cracks or damage.”
Before the accident on Tuesday afternoon, city planners had hoped the first metro trains would run on the new north-south line from Cologne's main train station in the historic centre to the rest of the U-Bahn network starting in 2010.
Search and rescue efforts intensified on Wednesday for a couple still missing after the building containing the archive and an adjacent apartment block collapsed.
"We believe there are currently two people still missing," said Cathrin Maus, a spokeswoman for the police in the western Germany city.
The pair lived in the adjacent building, according to Stefan Raphael, a spokesman for the fire service.
Two hundred fire fighters are still at the scene but the rescue operation is "very complicated and extremely difficult," officials said. Rescue workers built concrete ramps to enable vehicles to reach parts of the devastated site.
"We worked through the night," Raphael told news agency AFP.
Up to nine people were reported missing in the immediate aftermath of the collapse but several people have since been found safe and sound.
The four-storey building was evacuated shortly before it suddenly collapsed around 1 pm on Tuesday, city hall spokesman Gregor Timmer told AFP at the scene.
The archives housed 65,000 original documents dating from the year 922 as well as maps, films and photos and items left to the city by figures like composer Jacques Offenbach and Nobel Prize-winning author Heinrich Böll.
The building that collapsed had been in use as an archive since 1971. Officials will cover the archives with tarpaulins to protect from documents from the rain, the firemen said.
The cause of the collapse was unclear, but the former director of the archives, Eberhard Illner, said cracks had appeared in the building in recent weeks.
This was a "foreseeable catastrophe," he said.
News reports said that the disaster may have been caused by work taking place on the city's metro line in the area. But city officials said construction had ended some time ago.