The fire in a two-storey building in a small town in the Krasnodar Territory started at 01.11 a.m. local time (10.11 p.m. Monday GMT) and was put out four hours later.
According to latest reports, 97 people were in the building when the fire started. A total of 30 people have been hospitalized, the Ministry of Emergency Situations said.
The ministry said a late emergency call, staff misconduct and the remote location of the fire station contributed to the high death toll at the retirement home in the town of Kamyshevatskaya, located on the Sea of Azov coast.
Natalya Lukash, a spokeswoman for the ministry's information department, said the nearest fire station was 50 kilometers (31 miles) from the town, when it should have been no farther than three kilometers (around 2 miles) away.
She said it had taken the fire brigade almost an hour to get to the scene, and the first storey was engulfed by fire by the time they arrived.
Lukash said the janitor had twice ignored the fire alarm making an emergency call only when he saw flames.
She also said only four nurses had been on duty when the fire erupted and they were unable to properly evacuate the building.
The medical staff said 48 bedridden patients had been on the first storey.
Local prosecutors have opened a criminal case on manslaughter charges.
It was the latest in a string of fires that have hit medical institutions in Russia over the last several months. In December, a fire in a Moscow addiction clinic killed 46 people, and another 10 were killed in a fire in a psychiatric and neurological clinic in the Kemerovo Region in Russia's southwestern Siberia.
President Vladimir Putin declared March 21 a day of mourning for the victims of a West Siberian mine explosion, a plane crash on the Volga and the fire in the retirement home in southern Russia, the Kremlin press service said Tuesday.
A total of 107 people died in the explosion in the Ulyanovskaya mine in the Kemerovo Region March 19, six people were killed and more than 20 injured in the Tu-134 crash in Samara March 17, and 63 died in the fire at a retirement home in the Krasnodar Territory March 20.
Putin ordered that flags fly at half-mast and entertainment events and television programs cancelled across the country March 21.
He also ordered the government and local administrations "to establish a commission to investigate the causes of tragedies and to help the families of the victims."