A police chief told a 911 operator that he accidentally shot his wife early New Year's Day inside their suburban home southwest of Atlanta, investigators said Thursday.

Peachtree City Police Chief William McCollom called 911 around 4:15 a.m. and reported shooting his wife, Margaret, inside the couple's bedroom, Peachtree City Police Lt. Mark Brown said. McCollom's wife was flown to Atlanta Medical Center.

She was in critical condition, hospital spokeswoman Nicole Gustin said.

Investigators would not discuss what led McCollom to open fire. Local police turned the criminal probe over to the Georgia Bureau of Investigation and the local prosecutor's office.

GBI spokeswoman Sherry Lang said initial reports suggested that McCollom shot his wife twice, but later information revealed she was shot once. Authorities said the police chief fired his department-issued firearm, a 9-mm Glock handgun.

"He is fully cooperating at this point, and he has been interviewed," said Lang, who refused to comment on what McCollom told investigators.

The victim had not spoken police by early Thursday afternoon. It appeared there were no other witnesses to the shooting. Lang said GBI investigators believe McCollom and his wife were alone.

McCollom has been placed on administrative leave pending the outcome of the investigation and an internal review. He has not been charged with any crimes, said Scott Ballard, district attorney for the Griffin Judicial Circuit.

"There are a lot of things that we don't know yet about what took place that we need to know before we can make any decisions," Ballard said.

Police had never been summoned to the chief's home for an emergency prior to the shooting, Brown said.

The shooting surprised neighbors in the quiet subdivision about 30 miles southwest of Atlanta, and it left some on the city's police force shocked. McCollom has served as chief for about a year.

"If you think of someone you love so dearly, and you hurt the person you love so dearly, it's just tragic," said Terry Ernst, a city councilor who retired from the police department in 2012. He had spoken with several officers Thursday. "Everybody's just in disbelief."