Several floors, walls and part of the roof of a university building in St Petersburg collapsed on Saturday, trapping around two dozen people inside, according to Russia's emergency authorities.
80 people have now been evacuated from the building.
The cause of the partial collapse at the city's National Research University of Information Technologies, Mechanics and Optics (ITMO) remains unclear but the country's Emergency Ministry said that it occured while renovations were taking place.
Emergency services said there were no casualties, as no bodies were found in the rubble and no immediate injuries were reported.
"A partial roof collapse has occurred at one of the buildings; according to prelim. data, there have been no casualties," a spokesperson for the university said on Twitter.
"Emergency services and officials are on site."
Some students were reportedly at the university to attend elective weekend classes.
ITMO is one of Russia's national research universities.
Alexander Beglov, St Peterburg's acting governor, has travelled to the institution, according to state media.
Additional reporting by agencies
