A man carrying a gun entered the Procter & Gamble factory in the Gebze industrial zone in Kocaeli province around 3 p.m. local time (1200 GMT) on Thursday, according to media reports.
A police spokesperson was quoted by the AFP news agency as saying that the assailant's action was apparently in protest of Israel's war against Hamas in Gaza.
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 Turkish Demiroren news agency reported that police rushed to the scene and tried to persuade him to stand down, with special operation forces and medical personnel also dispatched.
Images from the scene showed police setting up a cordon around the sprawling plant, which primarily manufactures cosmetics.
Images circulated online appeared to show a man holding a weapon next to a drawing of the Palestinian flag and the words "for Gaza" painted on the wall in red.
Turkish President Recep Tayyip Erdogan has emerged as a harsh critic of Israel for the civilian toll of its campaign against Hamas militants. He's frequently accused Israel of genocide and referred to Hamas as "freedom figthers."
mf/sms (Reuters, AFP)