KNOXVILLE, Tenn. — Update 5:20 p.m.:

An air conditioner being serviced at Powell High School was what school resource officers heard Tuesday morning when they thought they heard gunshots outside, according to a letter Powell High School principal Chad Smith sent out. 

In the statement, Smith said there was an interruption to power to several parts of the school while crews worked on the air conditioner and as a result, several large crackling sounds were heard by school security personnel.

He explained that the officers did exactly what they were trained to do and as a result, the school was placed in a hard lockdown. 

"At approximately 10:26 a.m. while an air conditioner was being serviced at Powell High School, an electrical disruption occurred thus interrupting power to several parts of the school. As a result of this electrical disruption, several large cracking sounds were heard by school security personnel. Based on their training and their directive we went into a hard lockdown to ensure the safety and security of our students and staff. 

"I do want you to know that we had a very large and heavily armed police presence on campus. It is possible that your student could have seen one of the many armed personnel securing the building, which can be frightening. Please know that at no time, was your child in immediate danger and this was done so out of an abundance of caution.

"I would like to commend our students and staff on the way that they responded and followed our emergency protocols and plan. Additionally, I’d like to thank Sherriff Spangler and all of the responding officers, who quickly arrived at the scene to ensure our safety. 

"I know these events can be troubling. Situations like this can cause angst about coming to school and other public places. But please know that the safety of our students and staff is and will continue to be my number 1 priority.

"As a reminder, tomorrow is our first Late Arrival Wednesday of the Fall Semester and we look forward to seeing our students tomorrow morning as first block begins at 9:00 am. If you have any questions or desire additional support, feel free to contact us at 938-2171.

"Remember that We Love You and Go Panthers."

Original story:

Powell High School was placed on a hard lockdown Tuesday morning after a school resource officer said she heard what may have been shots fired outside the school, according to Knox County Sheriff's Office spokesperson Kimberly Glenn.

Knox County Sheriff Tom Spangler said he wanted parents to know their children were okay during a news conference around 11:30 a.m.

"I know it's been a tense and scary situation for everybody, obviously, because of everything that's been going on around this country," Spangler said.

Spangler said dispatch received reports of shots fired at the school at 10:27 a.m. after officers heard four to six "pops" that sounded like gunshots.

The school went into lockdown immediately in response. KCSO then searched the school and surrounding areas. By 11:30 a.m., the hard lockdown was lifted and parents were allowed to pick up their students. 

"The teachers had to lock the doors and we had to get under the desks," senior Greg Ballard said. "My heart was pounding."

He said he had done lockdown drills before to prepare for an active shooter situation. Still, this time felt different. 

"It just felt like something serious was happening," he said. "It was really starting to scare me."

Spangler said during the news conference that they have not yet found anything that could have caused the sound and they will continue to investigate.

KCSO will have a K-9 sweep through the school once students and staff have left, Spangler said.

"We feel good that there's nobody in there," he said.

Powell High School lockdown - parents pick up kids

Parents will be able to pick their children up at the community center if they wish to do so, but school will continue to be in session for the rest of the day, the sheriff's office said.

Parent Kelly Johnson Majors rushed to the scene when she heard her child's school was locked down.

"I needed to come see that everything's going to be okay," she said. "You think this will never happen to us."

She said her students had texted her from inside, letting her know they were okay.

"I have complete confidence in the total number of police that are here and handling the situation," Johnson Majors said.

Powell High School lockdown - parents pick up kids

There was a heavy police presence outside the school and a helicopter circling the school. Spangler said the department was using the helicopter to search nearby wooded areas to be sure no one was hiding there. 

Glenn said the sheriff's office has no confirmation that shots were actually fired.

"We don't know that shots were actually fired, we just have reports that shots were being fired," she said. 

Helicopter over Powell High School

Glenn also said she wanted parents to know that students are safe.

"We absolutely have this situation under control," she said as the building was being cleared. 

The Knoxville Police Department said it was also assisting with the investigation.

This is a developing story. 10News has crews on scene working to get more information.