The government’s disaster agency AFAD called the explosion an "industrial accident" in the district of Hendek in Sakarya province.
A total of 114 people were taken to the hospital and nearly 100 were discharged after the explosion in Sakarya province, Fahrettin Koca said on Twitter.
“We visited our patients who were injured in the blasts in Sakarya’s Hendek district and who are still under treatment. Of the 114 people who were hospitalized, 92 were discharged, and 22 were still on treatment,” Koca said.
“I wish God's mercy to the four citizens who lost their lives and I wish recovery for the injured ones,” the top doctor added.
A total of 84 ambulances, two air ambulances, 18 medical rescue teams, and emergency aid personnel along with disaster and emergency teams were dispatched to the scene where Koca said he would remain until he received updates about the wounded.
He said people living in the area might be affected by fireworks gases, especially in the first 12 hours after the blast and asked residents to wear masks and not leave their homes.
The factory has 186 employees, 20 of whom were not working Friday, and another 15 to 20 left work earlier in the morning.
Interior Minister Süleyman Soylu said three factory workers were still missing, adding that the resultant fire had been brought under control.
The ministers had been dispatched to the province by President Recep Tayyip Erdoğan.
Images on television earlier in the day showed a dark grey plume of smoke with sparks visible, a result of fireworks going off inside the building.
Hendek mayor Turgut Babaoğlu said many workers escaped the building during the incident.
Dozens of firefighters and rescue workers were mobilized after the explosion around 0815 GMT.
According to reports, there had previously been explosions at the factory in 2009, 2011 and 2014. One person died in the incident in 2014.
Warrants issued over blasts
Prosecutors in the northwestern Sakarya province issued warrants for the factory manager in charge and two foremen, said the sources on July 4, who asked not to be named due to restrictions on speaking to the media.
The investigation of the incident continues, the prosecutors reportedly said.