Russian rescuers are searching for people still trapped under the rubble of a city apartment block that partly collapsed in a suspected gas blast, killing at least four, according to the RIA news agency.
The blast took place at 4am local time on Monday (23:00 GMT) in the southern city of Magnitogorsk, RIA said.
At least 10 people have been rescued from the rubble, the news agency said, citing Russia‘s emergencies ministry.
News agency TASS said 68 people were unaccounted for, quoting Chelyabinsk regional Deputy Governor Oleg Klimov.
The emergencies ministry said the blast, probably caused by a gas leak, damaged 48 apartments.
National television broadcast footage of the mangled heaps of concrete as hundreds of rescue workers combed the debris in temperatures of minus 18 Celsius.
The Soviet-era high-rise was built in 1973 and was home to around 1,100 people. The residents have been evacuated.
A total of 110 people were registered as residents of the affected section of the building, regional authorities said. Sixteen of them have been evacuated, and another 15 were not home at the time of the blast.
In one sign of how serious the accident was, President Vladimir Putin was informed of the accident in the industrial city some 1,400km east of Moscow, according to the Kremlin.
There have been several similar incidents in Russia in recent years due to ageing infrastructure and poor safety regulations surrounding gas usage.
In 2015, at least five people were killed when a gas explosion damaged an apartment building in the southern Russian city of Volgograd.