At least three people were killed and another 79 people were unaccounted for after a gas explosion rocked a residential building in Russia's Urals city of Magnitogorsk on Monday, a senior official said.

"Three people have been pulled alive from the rubble and three are dead," Oleg Klimov, deputy governor of the Chelyabinsk region where the industrial city is located, was quoted as saying by state news agency RIA Novosti.

"The fate of 79 people is unclear," he said, adding police were working to locate their whereabouts.