CHARLOTTE -- At least a dozen people were rushed to the hospital following an apparent carbon monoxide leak early Wednesday morning at an uptown grocery store. One person was listed in serious condition.

Emergency crews responded to the Harris Teeter on Sixth Street around 5 a.m. after employees found a maintenance worker passed out in the back of the store. That person was taken to Carolinas medical Center-Main with a possible life-threatening condition.

A Harris Teeter spokesperson says the subcontractor was using a propane-fueled pressure washer to clean the drains inside the grocery store and became sick.

Of the 12 people taken to the hospital, four were firefighters and two were from Medic. No other serious injuries were reported.

After arriving at the location, Medic assessed the situation and determined that it was in fact a carbon monoxide leak.

“Monitors on the truck were able to signal that we had a carbon monoxide exposure here,” said Capt. Rob Brisley of the Charlotte Fire Department. “Additional firefighters and additional Medic trucks were brought so that everybody received quick treatment in a very dangerous situation.”

The Fifth and Poplar apartments, which sit above the Harris Teeter, were not evacuated as the location of the leak was pinpointed at the back of the store.

The North Carolina Department of Labor and the Mecklenburg County Health Department will be at the scene much of the day Wednesday to investigate exactly how the leak happened.