The explosion happened at 9.40 a.m. local time, causing a fire at a fuel depot at Chempark, an industrial park for chemicals companies including Bayer and Lanxess, Chempark operator Currenta said.
Several staff were hurt, with at least two seriously injured, and five people were missing, Currenta said, adding it was not yet clear what caused the explosion and the subsequent fire.
Sirens and emergency alerts on the German civil protection agency’s mobile phone app warned citizens of “extreme danger.”
Police asked nearby residents to remain indoors and keep doors and windows closed. Currenta said they should also turn off air conditioning systems while it measured the air around the site for possible toxic gas.
Several nearby motorways were closed, and police said drivers should take detours to avoid the area.
More than 30 companies operate at the Chempark site in Leverkusen, including Covestro, Bayer, Lanxess and Arlanxeo, according to its website.