A fire ripped through an overcrowded retirement home in central Russia overnight, killing 11 vulnerable people as the blaze swept through the small wooden building, investigators said Tuesday.

The Investigative Committee, which probes major crimes, said it had opened a criminal investigation into possible negligence over the blaze in the Bashkortostan region south of the Ural Mountains.

It released video showing columns of orange flame engulfing a one-storey wooden building during the night.

"At the time the fire started there were 15 people in the room, four of whom managed to escape on their own," the committee said in a statement. "In the course of extinguishing the fire, the bodies of 11 people were found," it added.

The victims -- seven men and four women -- were between 57 and 83 years old, according to local news website Ufa1.ru.

The emergencies ministry said it was notified about the fire at 02:53 am (2153 GMT) and that the flames were put out by 06:00 am.

In broad daylight images showed the house still standing, but with its walls blackened and its windows and roof blown out.

According to investigators the home in the village of Ishbuldino was registered as a non-profit organisation that provided care for the elderly.

But a local official told the Interfax news agency that it did not have the legal right to provide people with overnight accommodation.

The official added that the building, which was constructed in 1968 and was also fitted with a small attic, was not permitted to have more than 10 people in it at a time.

Different possible causes for the fire were being considered, the official said, including faulty wiring or human error like smoking a cigarette in bed.

"However, the fire alarm went off normally, which is why four people were able to escape," the source said.

No chance of surviving

On Tuesday, Bashkortostan regional head Radiy Khabirov said it was too soon to "guess what happened here" and asked for finger-pointing to be avoided "for now".

But he added: "I don't like that there were so many people in one small house," noting that "preventative measures" need to be taken.

Bashkortostan's labour and social protection minister Lenara Ivanova told the RIA Novosti news agency that the ministry had no information about the home, adding that it was a private organisation.

The TASS news agency, citing a law enforcement official, reported that the director of the nursing home had been detained.

Village resident Ayslu Khamziyeva said in an interview with the REN-TV television channel that residents of the home had no chance of surviving.

"They were all bed-ridden people," she said, adding that she and her brother started waking neighbours and dousing the house with water when they noticed the fire.

Accidental fires and blasts in residential buildings are relatively common in Russia as a result of ageing infrastructure and non-compliance with safety standards.

Local news website URA.ru on Tuesday reported that in the past week 197 fires had taken place in Bashkortostan, including one that killed four people.

Earlier this spring, two separate fires at retirement homes in Moscow and the Moscow region killed at least 15 people.