Private NTV television said the explosion was close to a park that is home to a landmark obelisk.
Ambulances rushed to the scene of the explosion in Sultanahmet square, close to the Blue Mosque and Hagia Sophia, in a major tourist area of Turkey’s most populous city.
Police sealed the area, barring people from approaching in case of a second explosion.
Turkey has been on alert for attacks since an October double suicide bombing killed more than 100 people at a gathering of peace activists outside a train station in the capital, Ankara.
The government cancelled planned New Year’s celebrations in Ankara after detaining two suspected Islamic State members believed to be planning suicide attacks.
Turkish forces have also been carrying out an offensive against the outlawed Kurdistan Workers Party, which has been blamed for attacks including those targeting police and soldiers.
(source: VOA with iformation from NTV, AP, Reuters)