"It's not certain whether one person remains under the debris. Rescue teams are searching meticulously," Istanbul police chief Selami Altinok told reporters at the blast site.
Rescue teams dug a body from the debris some seven hours after the explosion, media reports said.
The accident was caused by either a gas leak or an exploding gas canister, Istanbul Governor Huseyin Avni Mutlu said, ruling out the possibility of a terrorist attack.
On Friday, one person died and 36 were injured in a gas explosion at a bakery in the city of Denizli, southwestern Turkey, the disaster management agency said.