Part of the roof and several floors of a university building in Russia’s second-largest city have collapsed, with no casualties.

The Russian emergencies ministry said the collapse at the Saint Petersburg National Research University of Information Technologies, Mechanics and Optics took place while construction work was under way.

An investigation into the possible criminal violation of construction safety has been opened.

St Petersburg’s acting governor Alexander Beglov told journalists at the scene in the central city that 81 people were evacuated from the building.

He said there were no injuries.

Mr Beglov said about 20 of those evacuated were foreign students attending a weekend class.

The school, known as ITMO University, is one of Russia’s national research universities.