Rescue teams were searching for more victims under the rubble, Sakhalin Gov. Valery Limarenko wrote on Telegram. Some of the 33 people known to have lived in the building remained unaccounted for, he said.
Sakhalin is located in the Pacific Ocean, north of Japan.
According to Limarenko, residents affected by the explosion were offered temporary shelter and families who lost their homes will be paid 500,000 rubles ($8,217). Relatives of the people killed can expect to receive 1 million rubles ($16,434), he said.