Five children were crushed to death on Wednesday when a concrete stairwell collapsed at their three-storey school in central Russia, emergency officials said.

"Five people were killed and four injured," when the stairwell gave way during repairs, emergency situations ministry spokesperson Tatyana Khvatkova said in televised comments.

Eleven people were pulled from the rubble and 800 were evacuated from the school, located near the city of Orenburg in the Russia's Urals region, she said.

Rescuers lifted large slabs of concrete as they searched through the rubble at the foot of a gaping hole in the school building, television pictures showed.

The dead children were all in the 11th grade, the Interfax and RIA Novosti news agencies reported, citing emergency officials.

Investigators are studying the incident for evidence of criminal negligence in the repairs.

A regional safety official said the collapse occurred when workers removed a window frame from a part of the building near the set of stairs, Interfax reported.

Deadly accidents and fires are common in Russia partly due to ageing infrastructure and lax enforcement of safety regulations.

AFP