A car bomb went off outside a police headquarters in south-eastern Turkey on Sunday, killing one policeman and wounding 13 people, state news agency Anadolu reported.
Nine police officers were among the injured in the attack in Gaziantep, the report cited the governor as saying.
The DHA news agency said shots could be heard after the explosion.
Anadolu and DHA described the May Day blast as a "terrorist attack."
German Chancellor Angela Merkel was in Gaziantep on April 23 to visit a camp for Syrian refugees. Gaziantep province borders Syria.
Security measures have been tightened across Turkey on May Day in anticipation of protests.