The two blasts went off minutes apart at around 10:00 p.m. local time (19:00 GMT) in the city's Gungoren district.
The first bomb, planted in a rubbish container in a residential area, caused a minor explosion that injured several bystanders. After onlookers rushed to the scene to help those injured, a second, more powerful blast went off a few meters away in the middle of the gathering.
NTV reported that seven people are in a critical condition.
Turkish media cited police sources as saying the attack bears the hallmarks of the separatist Kurdistan Workers Party (PKK). The Turkish military has carried out several major operations recently against the rebel group's bases.
"There is no doubt that this was a terrorist attack," Governor Muammer Guler told reporters.
No groups have yet claimed responsibility for the attack in Turkey's largest city, the most deadly to hit the country in almost five years.
The PKK has been fighting for an autonomous ethnic Kurd state in southeast Turkey for nearly 25 years. The conflict has so far claimed over 40,000 lives.
The attack was the most severe to hit the country since bombings on November 15 and 20, 2003, which left a total of 57 dead. Al Qaeda claimed responsibility for the blasts, the worst of a series of explosions blamed on Islamic extremist groups that year that killed more than 60 people.
