An explosion near an Istanbul police station on Thursday was caused by a "motorcycle bomb blast" and wounded five people, one of them seriously, provincial governor Vasip Sahin wrote on Twitter.
Reports say the cause of the blast near the police station in Yenibosna district was not immediately known.
Many ambulances were dispatched to the scene, it added. Television pictures showed several cars wrecked and shards of glass scattering the ground after the blast.
Witnesses told CNN-Turk that they heard a powerful explosion as well as gunshots. Turkish police sealed off the area on suspicion of a possible second blast.
The force of the blast blew out the windows of the police station.
Turkey has already been hit by a bloody year of militant attacks in its two biggest cities that have left dozens of people dead and put the country on a high security alert.
Kurdish militants have twice struck in Ankara in deadly attacks, while suspected ISISsuicide bombers have on three occasions struck in Istanbul.