At least 23 people were killed in a blaze at a psychiatric hospital in Russia's Voronezh region, the emergency situations ministry said on Sunday.

Two more died in the hospital after rescuers recovered 21 bodies from the building, Tass news agency quoted an official from emergencies ministry as saying.

Over 90 people were inside the psychiatric hospital when the fire broke out on Saturday night.

At least 51 people were evacuated from the building, and 21 people with burns of various degree were hospitalised.

All the dead were bedridden patients, a law enforcement official said.

The fire has been put out, but its cause remains unclear.

A preliminary investigation into the tragedy has been launched by Russia's Investigation Committee.