Originally Published: 27 MAR 23 12:13 ET

Updated: 27 MAR 23 14:56 ET

By Eric Levenson and Jennifer Henderson, CNN

(CNN) -- A 28-year-old woman fatally shot three students and three adults at a private Christian school in Nashville before she was shot and killed by police, authorities said.

The shooter, who has not been identified, entered the Covenant School via a side door and was armed with at least two assault-style rifles and a handgun, said Metro Nashville Police spokesperson Don Aaron. She fired multiple shots on the first and second floors of the school before police fatally shot her on the second floor, Aaron said.

The first call on the shooting came in at 10:13 a.m. and the shooter was dead at 10:27 a.m., he said.

One police officer who responded to the scene was wounded from cut glass, he added. There were no other people wounded.

Police initially said the shooter appeared to be in her teens but later identified her as a 28-year-old Nashville woman.

The Nashville Fire Department tried to provide lifesaving efforts to those with "viable signs of life" and transported the three children along with two adults from the scene, Fire spokesperson Kendra Loney said. They did not survive.

The incident is the 19th shooting at a school or university so far this year in which at least one person was wounded, according to a CNN tally. Last week, two faculty members were shot and wounded by a student at a high school in Denver, and the student was later found dead of a self-inflicted gunshot wound.

With six victims, Monday's attack is the deadliest school shooting since the heinous attack in Uvalde, Texas, last May that left 21 people dead.

The Covenant School is a private Christian school founded in 2001 as a ministry of Covenant Presbyterian Church and teaches preschool through 6th grade, according to its website. On a typical day it has 209 students and 40 to 50 staff members, Aaron said.

"The beauty of a PreSchool-6th school is in its simplicity and innocence," the school says on its site. "Students are free to be children -- they can feel fully and safely known by our faculty and become leaders under their guidance."

Concerned loved ones gathered outside school

The mass shooting garnered a massive police and fire response, and concerned families gathered outside the school to wait for word of their loved ones.

Avery Myrick, whose mother is a teacher at the school, told CNN affiliate WSMV her mom texted that she was hiding in a closet and could hear shooting all over the school. She later spoke to her mother on the phone and learned she was safe.

"Just getting that initial phone call that she was OK, it obviously brings a ton of relief, but you're still hurting for the people out there who may not get that call," she said.

Jozen Reodica, who works at Shearwater Health across the street from the school, took video of police escorting students out of the school on Monday. In the video, the children are holding hands and walking in a line down the street.

She told CNN she realized something was wrong when she saw several police cars arrive at the scene.

"They (police) started to close down the roads. It happened so fast. I saw a policeman run to the scene and then after few minutes kids were already crossing," Reodica said.

Nashville Mayor John Cooper offered his condolences in a statement.

"In a tragic morning, Nashville joined the dreaded, long list of communities to experience a school shooting. My heart goes out to the families of the victims. Our entire city stands with you. As facts continue to emerge, I thank our first responders and medical professionals," he said.

President Joe Biden said in a news conference the shooting was "sick" and "heartbreaking" and urged Congress to take further action on gun safety legislation.

White House press secretary Karine Jean-Pierre also called on lawmakers to pass laws addressing gun safety.

"How many more children have to be murdered before Republicans in Congress will step up and act to pass the assault weapons ban, to close loopholes in our background check system, or to require the safe storage of guns? We need to do something," she said.

This is a developing story and will be updated.