It was not immediately clear how many people were being held at the plant, which lies on the eastern outskirts of Turkey's largest city, the spokesman told AFP.

A union representing workers at the consumer goods plant said the assailant was holding seven people hostage, adding that the rest of the plant's workers had been released.

The private DHA news agency published a photo widely circulated online of the alleged assailant holding a gun and what appeared to be a suicide vest strapped to his chest.

The man was standing next to a drawing of the Palestinian flag and the words "for Gaza" painted on the wall in red.

Images from the scene showed police setting up a cordon around the sprawling plant, which primarily manufactures cosmetics.

Special operation forces and medical personnel were dispatched to the scene, Turkish media reported.

The health ministry in Gaza said Thursday at least 27,019 people have been killed in nearly four months of war. 

A ministry statement said some 66,139 people have been wounded in Gaza since Israel launched an offensive on Hamas.

Turkish President Recep Tayyip Erdogan has emerged as one of the Muslim world's harshest critics of Israel for the massive toll of its reprisal campaign against Hamas militants.

He has branded Israel a "terrorist state" and compared Israeli Prime Minister Benjamin Netanyahu to Adolf Hitler.