At a press conference on Wednesday, he urges people in the area not to touch soot flakes or other residues from the fire, as they can be toxic.
Residents are advised not to eat fruit and vegetables from their gardens and nearby playgrounds have been closed.
"Will get to the bottom of the event"
Two people have previously been confirmed dead after the incident in which 31 people were injured.
The cause of the explosion, which was heard several kilometers away, is still unclear.
The police in Cologne are investigating whether anyone has committed murder through negligence.
- We will do everything in our power to get to the bottom of this terrible event, says Frank Hyldmar.
Leverkusen is located in a densely populated metropolitan region around Cologne.
The company Currenta states that the explosion did not occur in the industrial area itself, but in a separate part of the area where waste is deposited or incinerated.