UPDATED 1.39PM: A fire that ripped through one of Russia's largest university libraries is believed to have damaged over one million historic documents.

The blaze, which started on Friday and was still not completely out on Saturday evening, ravaged 2000 square metres of the Institute of Scientific Information on Social Sciences in Moscow.

The library was created in 1918 and holds 10 million documents, some dating back to the 16th century.

"It's a major loss for science. This is the largest collection of its kind in the world, probably equivalent to the (United States) Library of Congress," Vladimir Fortov, president of the Russian Academy of Sciences was quoted as saying by Russia press agencies.

"One can find documents there that are impossible to find elsewhere.

"What has happened here is reminiscent of Chernobyl," he said referring to the 1986 nuclear catastrophe.

Fortov said about 15 per cent of the collection had been damaged, which includes one of the world's richest catalogues of Slavic language works but also documents from Britain, Italy and the US.

Fortov said much of the damage was caused by the water used by firefighters.
No one was injured in the inferno.

The fire broke out on Friday evening on the library's second floor and continued burning despite 200 firefighters' efforts.

Library authorities initially said the documents were not in danger but once the fire caused 1000 square metres of the roof to collapse they were less certain.

Authorities said it was impossible to remove the books because of intense heat.

Investigators are said to be looking into an electrical short-cicuit as the cause.