Search crews have pulled more bodies from a huge pile of rubble at a collapsed Russian apartment building, bringing the known death toll to 21.

The bodies found on Wednesday in Magnitogorsk included a 3-year-old girl, Russian news agencies cited the emergencies ministry as saying.

An 11-month-old boy who was pulled alive from the wreckage on Tuesday nearly 36 hours after the building collapsed was in serious but stable condition in a children's hospital in Moscow. He was flown about 1 400km to the capital in a plane dispatched by the Health Ministry.

Health Minister Veronika Skvortsova said on Wednesday that the boy suffered superficial head wounds but no apparent brain damage.

More than 20 people who lived in the building remain unaccounted for, including five children.

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