"There are three injured and six dead," said the health ministry in the Udmurtia region of which Izhevsk is the capital.
The sixth body was discovered earlier Friday, an emergencies ministry official told AFP.
"A woman has been found in the building's basement," the official said, adding that a search and rescue operation continued.
One of the six victims was a child, officials have said.
The incident happened on Thursday afternoon when a corner section of the Soviet-era residential block collapsed after what was believed to be a gas explosion.
Video footage showed flats on all nine floors reduced to debris. A total of eight apartments are believed to be completely destroyed.
More than 200 rescuers have been involved in the search for survivors.
Izhevsk, which is home to some 650,000 people, is located some 940 kilometres (585 miles) east of Moscow.
Explosions caused by gas leaks are frequent in Russia, especially in older Soviet-era buildings.
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