The blasts took place near the city's central train station. The target appears to have been a march, organized by leftists groups, calling for an end to the violence with the Kurdish separatist group, the PKK.
Read more: 30 people killed in suspected suicide bombing in Turkey
Turkish news agency Dogan said that at least 20 people have been killed, but the number was expected to rise as rescue efforts continued. TV footage shows scenes of panic and people lying on the ground covered in blood, amid protest banners.
Government officials say the blasts were a terrorist attack and are investigating reports that a suicide bomber was behind at least one of the explosions. The leader of the pro-Kurdish HDP party has blamed the state for the attack, and cancelled all election rallies.