The two blasts, minutes apart Sunday afternoon, injured at least 154 people, reported Anadolu, the Turkish state news agency.
Istanbul Gov. Muammer Guler called the blasts "an act of terror."
The bombs were about 50 feet from each other, Guler said. The first in a telephone booth was a stun grenade detonated to draw attention before the second blast went off in a trash bin as a crowd gathered, he said.
Guler said police launched an investigation into who is responsible for the blasts that occurred in Istanbul's Gungoren community.
No one had claimed responsibility as of late Sunday, CNN reported.