CHICAGO (CBS) — Five people, including a six-year-old girl, were hospitalized after elevated carbon monoxide levels were discovered overnight at a home in the Bronzeville neighborhood.

A Chicago Fire Department spokesperson said crews responded to reports of high carbon monoxide readings at a home near 48th and Evans shortly after midnight.

Carbon monoxide levels on the first and second floors were 450 parts per million, while levels in the basement were 800 ppm.

According to the U.S. Consumer Products Safety Commission, levels above 70 ppm are considered dangerous, and sustained concentrations above 150 ppm can cause disorientation, unconsciousness, or death.

Five people in the house were hospitalized. A six-year-old girl was taken to Comer Children’s Hospital in serious to critical condition. A 70-year-old woman, a 45-year-old woman, and a 17-year-old boy were taken to the University of Chicago Medical Center in fair to serious condition.

A 65-year-old man was taken to Mercy Hospital & Medical Center in good to fair condition.

The cause of the elevated carbon monoxide levels was unknown.