The blast took place in the heart of the bustling city centre, between the ruling AKP's offices and those of the governor, Anadolu added.
It was not immediately clear who was behind the blast, which initially appeared to have been caused by a car bomb.
Television images showed water cannon being used to put out a fire caused by the explosion.
Witnesses said the force of the blast shattered the windows in the surrounding vicinity. Several ambulances rushed to the scene.
The blast came a day after the government announced the removal of 28 mayors, mainly over alleged links to the outlawed Kurdistan Workers Party (PKK) in a move strongly denounced by pro-Kurdish parties.
The PKK is listed a terror group by Turkey and its Western allies.
The government has stepped up its military campaign in the restive southeast to eradicate PKK militants, who have launched almost daily attacks since the rupture of a fragile ceasefire last year.
Tens of thousands of people have been killed since the PKK first took up arms in 1984, with the aim of carving out an independent state for Turkey's Kurdish minority, AFP reports.
Turkey has also launched an operation inside Syria to remove Islamic State (ISIS, ISIL) group militants as well as Syrian Kurdish militia from its frontier.
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