An unidentified suspect fired multiple rounds at a security officer on patrol at the Watts Bar Nuclear Plant early Sunday morning, and at least one round hit the security officer’s vehicle, an official said.

The Tennessee Valley Authority nuclear security officer fired back, also shooting multiple rounds.

The suspect appeared to have initially been on the ground but may have fled in a boat, TVA spokesman Jim Hopson said.

The shots were fired just after 2 a.m. this morning on the east side of the 1,700-acre plant, near the Tennessee River, toward the plant’s southern boundary, TVA said. The officer was several hundred yards outside the protected area where the reactor and power equipment are located.

Hopson said some information can’t be released yet, such as the identity of the security officer, or it is not available, such as the total number of rounds fired. Hopson didn’t have a description of the suspect.

“Many of the details I won’t be able to share,” he said. “The investigation is still ongoing.”

TVA declared an “unusual event,” the lowest of the four Nuclear Regulatory Commission emergency classifications.

“There was no threat to public safety during the incident and no threat to the security of the plant due to the location outside of the plant perimeter,” TVA said in a Sunday morning statement. “An investigation is under way.”

TVA said the plant remains under a heightened state of security.

“Local law enforcement agencies are assisting TVA Police with the investigation,” TVA said. “The Nuclear Regulatory Commission and appropriate state and federal agencies were notified, and the NRC has staffed its incident response center in the Region II office in Atlanta and is monitoring the events, along with the resident inspector who has responded to the site.”

Hopson said it appears that only the suspect and the security officer were involved.

It’s the first time since Watts Bar began operating in 1996 that a nuclear security officer has exchanged gunfire with a suspect at the site.

The Watts Bar Nuclear Plant is near Spring City, which is about 45 miles southwest of Oak Ridge. It’s in Rhea County south of Watts Bar Lake and on the north end of Chickamauga Lake. The plant has one 1,100-megawatt unit that is already operating, and a second is under construction.

Note: This story was last updated at 9:05 a.m. April 23.