According to reports, the explosion took place in İzmir's Buca district at around 8 a.m. local time.
Suspected terrorists reportedly detonated the bomb as the shuttle bus was passing by Ahmet Piriştina Boulevard, Doğan News Agency said.
Security forces and ambulances were dispatched to the scene of the explosion.
Police have launched an investigation to find perpetrators.
On Monday, PKK terrorists killed three construction workers in Turkey's southeastern Şırnak province.
More than 1,200 people, including security personnel and civilians, have lost their lives since the PKK -- listed as a terrorist organization by Turkey, the U.S. and the EU -- resumed its decades-long armed campaign in July 2015.