CHARLOTTE, N.C. — Authorities said a shopping mall in North Carolina had to be evacuated and four people were taken to hospitals because of possible monoxide poisoning.

Firefighters were called to SouthPark Mall in Charlotte around 9 p.m. EDT Thursday because of hazardous conditions, the Charlotte Fire Department said. Fire Capt. Jackie Gilmore said on the department’s Twitter account that firefighters were monitoring carbon monoxide levels.

He said some 40 firefighters responded. There was no immediate indication of what caused the problem.

Officials have not released the names or conditions of those taken to the hospital.

No other details were immediately available Friday morning. A fire department spokesman did not immediately return a call seeking more details.