Complicating efforts is the extreme instability of the site, the Cologne fire department said on Sunday. Several neighbouring buildings are in danger of collapse and rainfall expected on Sunday could make the rubble even more unstable.
Rescue services are building an emergency roof over the site to prevent more moisture from seeping into the debris, which also contains priceless artefacts detailing the city's long history.
Authorities said the body would be identified later today at a morgue in Cologne. The two young men are thought to have died in the accident, when their apartments in neighbouring buildings also collapsed with the archive. One of the men is believed to be a 17 year-old baker's apprentice, the other a 23-year-old design student.
There is speculation the construction of a subway tunnel in front of the archive building may have contributed to its collapse. The site reportedly had repeated problems with groundwater leaking into the tunnel, which could have weakened the building's foundations.