The Walmart, located at 4461 New Bern Avenue, was evacuated while authorities investigated.
There were reports of some sort of haze in a bathroom inside the store. The company said a plumber mixed two chemicals in a urinal, creating the hazardous fumes.
The Walmart reopened to customers just before 2 p.m. Fire and hazmat crews are no longer on the scene.
Correction: An earlier version of this story stated seven people were taken to the hospital. EMS later told ABC11 the correct number was nine.
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