ST. LOUIS COUNTY, MO (CNN/KSDK) -- A Missouri Walmart was evacuated Thursday evening after a mobile meth lab was found cooking inside the Saint Louis County store.

Police said the woman responsible was first detained by employees for shoplifting. The suspect was placed in custody inside the store.

That's when police say she began brewing the explosive drug inside a 20-ounce bottle. Lt. Mark Cox says, "It's a very volatile situation and this one certainly was. It was in production and the sergeant on the scene that helped dismantle it, said it was currently cooking when they showed up. It had the potential to become flammable and blow up at any time."

Police said they found even more chemicals to make the drug when they searched the suspect's vehicle. A hazmat team also responded to clean up the holding room.