The Georgia Bureau of Investigation said at least four people were killed and nine others were injured after students were evacuated Wednesday from Apalachee High School in Winder, Ga., following a school shooting. A suspect is in police custody.

All schools in Barrow County, near Atlanta, were placed on lockdown after an unspecified threat, local officials said. Multiple casualties have been reported, but the number of victims and details of their conditions have not yet been confirmed.

At around 10:20 a.m. ET, officers from multiple agencies and emergency personnel were dispatched to the school after reports of an active shooter. About an hour later, the school was evacuated and students were taken to their families. Police and emergency responders were seen on campus, with at least two people being put on helicopters to be flown to hospitals, local news channel WSB-TV reported.

The FBI’s Atlanta office also said it was cooperating with the investigation into the events at the school.

School officials and the Barrow County Sheriff’s Office did not immediately respond to Yahoo News requests for comment.

A 17-year-old student told ABC News that he was in chemistry class when he heard gunshots. He said his chemistry teacher locked the door while the rest of the class gathered in the back. The student said he heard gunshots and screams, and at one point someone banged on the classroom door and yelled “open up” several times. The student and his class were later evacuated to the soccer field.

During a brief news conference Wednesday afternoon, Barrow County Sheriff Jud Smith called the investigation “very, very fluid” and in its early stages. Smith confirmed “multiple injuries” but did not provide a specific number or details on the severity of the injuries.

“What you see behind us today is something bad,” he said.

President Biden released a statement following the shooting, saying: “What should have been a joyous start to the school year in Winder, Georgia, has now turned into yet another horrific reminder of how gun violence continues to tear our communities apart. Students across the country are being taught how to duck and cover instead of how to read and write. We can no longer accept this as business as usual.”

Attorney General Merrick Garland told reporters he was “devastated” by the “terrible tragedy.”

“We are still gathering information, but the FBI and ATF are on the ground and working with partners at the state, local and federal levels,” Garland said. “The Department of Justice stands ready to provide resources or support to the needs of the Winder community in the coming days.”

Georgia Governor Brian Kemp, “I have deployed all available state resources to respond to the incident at Apalachee High School and urge all Georgians to join my family in praying for the safety of those in our classrooms, both in Barrow County and across the state. We continue to work with local, state, and federal partners as we gather information and continue to respond to this situation.”

This is a developing story. Check back here for updates.