The fire Monday was caused by welding sparks that ignited cotton cloth being stored at a facility run by the firm Kaixinda, authorities said.
Two of the company's employees and two from a clothing firm were detained, Anyang Mayor Gao Yong told reporters late Tuesday, according to state media. They have not been formally arrested and there was no immediate word on what charges they may face.
In addition to the dead, two people were injured in the fire that took more than four hours to extinguish.
Gao said the city would thoroughly inspect all possible safety risks in the city of more than 5 million people in the central province of Henan.
"This accident has taken such a huge toll on human life, the lessons must be understood at a very deep level," Gao was quoted as saying.
Densely populated and economically prominent Henan has seen a number of recent deadly incidents blamed on violations of safety regulations and lax government supervision.
Five officials were arrested after a building collapse that killed 53 people on the outskirts of Henan's provincial capital Changsha in April.
The central government has pledged stronger safety measures ever since an explosion in 2015 at a chemical warehouse in the northern port city of Tianjin killed 173 people, most of them firefighters and police officers. In that case, a number of local officials were accused of taking bribes to ignore safety violations.