Palm Harbor Fire Rescue evacuated the Walmart at 3801 Tampa Road in Oldsmar on Wednesday, Nov. 11, after crews detected high levels of carbon monoxide inside the store.

All employees and customers were cleared from the building, according to WTSP. No injuries were immediately reported.

The incident began when fire crews responded to the store for a medical emergency and a carbon monoxide monitor registered high readings while they treated a patient, the Oldsmar Fire Department told FOX 13. That triggered the full evacuation.

Palm Harbor Fire Rescue said in a news release that the leak occurred "following overnight welding operations," according to the Tampa Bay Times. FOX 13 reported it was not immediately clear whether the welding was connected to the elevated carbon monoxide readings.

The store's size made clearing the air a major operation. "Due to the size of the facility, ventilation operations are extensive," Palm Harbor Fire Rescue said in the release, as reported by WFLA.

The Hillsborough County Sheriff's Office Marine Unit brought in airboats to help push air through the building, FOX 13 reported. Units from Oldsmar Fire, Palm Harbor Fire Rescue, East Lake, Sunstar, the Pinellas County Sheriff's Office and the Hillsborough County Sheriff's Office were all on scene.

Nobody knew when the store would reopen.

Palm Harbor Fire Rescue asked drivers and residents to avoid the Tampa Road area while emergency operations continued.