Moscow (CNN)More than 1 million historic documents have been destroyed in a fire at one of Russia's largest public libraries, according to the Russian state news agency Tass. 

The Russian emergency situations ministry says 147 firefighters struggled for 25 hours over the weekend to put out the blaze in the main library of the Institute for Research Information on Social Sciences in Moscow. 

The fire, which ripped through the library Friday evening, destroyed 2,000 square meters (about 2,400 square yards) of the building and caused part of the roof to collapse, according to an official statement. The Russian emergency situations ministry said the fire was particularly hard to put out because of the high temperatures, narrow passageways and the risk of the building falling down. 

Moscow's emergency ministry said the temperature inside the rubble of the library remains high and that there is still a threat that the building could collapse. 

Vladimir Fortov, president of the Russian Academy of Sciences, told the Russian news agency RIA Novosti that the fire, which destroyed 15% of all the documents in the library, reminded him of the 1986 disaster at the Chernobyl nuclear plant in Ukraine. 

"It's a major loss for science. This is the largest collection of its kind in the world, probably equivalent to the Library of Congress," Fortov told the agency. "It contains material that you can't find anywhere else and all the social science institutions use this library. What has happened here is reminiscent of Chernobyl." 

The institute's director, Yuri Pivovarov, told Tass that he fears the building cannot be restored. 
How many were there?
 147 firefighters