Rescuers searched for two people feared trapped under the rubble of a collapsed archive building in the German city of Cologne on Wednesday and tried to save documents worth hundreds of millions of euros.

The multi-storey building containing thousands of historical records collapsed on Tuesday, injuring at least one person.

Officials said two men living in the building next to the town archive were missing, adding several other people who had also been reported missing had been accounted for.

The reason for the collapse of the 1970s building was unknown, officials said, but Cologne's Mayor Fritz Schramma suggested work on an underground train line near the building would be examined closely.

"(The question is) whether you can remove such chunks of earth beneath a city as big, as inhabited and as busy as Cologne has been for 2,000 years," he said as he visited the site of the collapse, where workers tried to stabilise the remains of the building.

The head of Cologne's cultural department, Georg Quander, said the collapse was threatening documents representing 1,000 years of history with an insurance value of 400 million euros.

The historical town archive was one of the biggest of its kind in Germany. Among them were many documents belonging to the late Nobel Prize winning German author Heinrich Boell.

"As disastrous as this is, we're grateful that all staff, guests and readers were able to get out," Quander said.

"Everything started with a crash. Three minutes later the building collapsed. Within that time, everyone was able to get out," he told a news conference.

Quander said the cultural loss linked to the collapse risked being larger than the one caused by a fire at the Anna-Amalia library in Weimar, which destroyed thousands of books in 2004.