The historic main building of the Library of Congress was evacuated for a time Tuesday night, the U.S. Capitol Police said.

A water alarm went off in the Jefferson building, said Lt. Kimberly Schneider. Parts of First Street and East Capitol Street were blocked off as emergency vehicles responded.

The evacuation was carried out as a precaution, but an all clear was given after about an hour or two, authorities said.

It was not immediately clear what had triggered the alarm. No information was available immediately about the extent of any damage in the building. In addition to a large book collection, it houses artistic, historic and cultural treasures.