According to the Milliyet newspaper, the explosion went off in a residential building in the Kadikoy district and caused a fire. Several fire and police brigades along with ambulances were called to the scene. The fire has been put under control.
Other news outlets report that one person was injured as a result of the blast.
Local authorities confirmed the incident later on Sunday, adding that three people died as a result of what appears to be a natural gas explosion.
"Unfortunately, three people lost their lives in the natural gas explosion in Kadikoy," Istanbul's governor Ali Yerlikaya said on Twitter.
Search and rescue operations in the building continue, the official added.