Censor.NET reports citing BBC.
The blast hit the southern city, 10km (six miles) from the Syrian border, at about 09:30 local time (06:30 GMT).
CNN Turk said the blast was heard several kilometres away.
Nine of the injured were police officers, Gaziantep's regional governor was quoted as saying.
Some reports said gunfire was heard after the blast. There was no immediate word on who is behind the latest blast.
Gaziantep is known to have several IS cells.