Story highlights The fire also left 23 people injured

It started late Saturday night and engulfed hundreds of square kilometers

(CNN) A fire killed 23 people and injured another 23 at a Russian psychiatric hospital, authorities said Sunday.

The blaze started late Saturday night at the hospital in the southwestern region of Voronezh.

Hospital workers told state-run media there were 140 people in the building, including 50 who were bedridden.

An investigation is underway.

Russia's Ministry of Emergency Situations said the fire has been extinguished. Search-and-rescue teams were surveying the site and inspecting the building.