At least five people died after a gas explosion ripped through an apartment block and set it ablaze in the southern Russian city of Volgograd on Sunday, Interfax news agency said, citing local authorities.
The Russian Investigative Committee, which reports directly to President Vladimir Putin, has said around 150 people lived in the affected section of the nine-storey building.
A local Emergency Ministry official was quoted as saying that 10 to 12 people could be trapped beneath the debris.
Local TV showed footage of fire-fighters trying to put out the fire, and of the building's heavily damaged facade.
Gas blasts are relatively common in Russia, where Soviet-era infrastructure is ageing and safety requirements are often ignored.
Just a week ago a fire swept through a psychiatric clinic in a village in the Voronezh region south of Moscow killing 23 people.
In one of the biggest such incidents, 58 people died in March 2004 in Northern city of Arkhangelsk.