(CNN) — Four people were killed in Tulsa on Wednesday after a gunman — who was later found dead — opened fire on the second floor of a medical building, authorities in Oklahoma said.

“It was just madness inside, with hundreds of rooms and hundreds of people trying to get out of the building,” Tulsa police Capt. Richard Meulenberg told CNN.

The mass shooting is among the latest instances nationwide of first responders and civilians coming face-to-face with the threat of gun violence in public places. It comes more than two weeks after a racist assault at a supermarket in Buffalo, New York, and a bloody attack at a church in California; and eight days after a heartbreaking massacre at an elementary school in Uvalde, Texas.

Law enforcement received a call just before 5 p.m. Wednesday about a person with a firearm at the Natalie Medical Building, a physicians’ office facility on the campus of Saint Francis Hospital, Tulsa police Deputy Chief Eric Dalgleish said at a news conference.

Responding officers who arrived within minutes “were hearing shots in the building, and that’s what directed them to the second floor,” Dalgleish said.

The gunman was found dead by police as they worked their way inside the building, Meulenberg said, and has not been publicly identified.

Police suspect the gunman’s fatal wounds were self-inflicted, and two firearms — described by Meulenberg as a semiautomatic rifle and a semiautomatic pistol — believed to have been used in the shooting were found next to him. Two of the deceased were found in the same room as the gunman, the police captain said.

It was unclear whether the four people killed were medical staffers, patients or visitors, said Dalgleish, who said the shooting took place at an orthopedic center in the building.

In addition, fewer than 10 people suffered non-life-threatening injuries, Meulenberg said. Authorities are trying to determine if they were wounded by gunfire or during the chaos of escaping the scene, he said. No officers were injured.

Investigators are working to determine the gunman’s motive, although the shooting was not believed to be indiscriminate, Meulenberg told CNN’s Don Lemon.

“He very purposefully went to this location, went to a very specific floor, and shot with very specific purpose,” he said. “This was not a random shooting by this individual.”

Witnesses describe frantic first moments

Lachelle Nathan told CNN affiliate KTUL that she had arrived in her vehicle with her daughter-in-law and grandchildren for a doctor’s appointment when she saw multiple officers race toward the complex.

“It’s awful, it’s sad. My daughter-in-law is from Buffalo, so now it’s so close to home. It’s not even safe if you come outside anymore, you know?” Nathan said.

“I mean, you see it on TV,” her daughter-in-law said, “but you don’t think it’s actually going to happen right in front of your eyes, so this is a wakeup call for my kids, this can really happen anywhere and it’s very scary.”

“You can’t even go to a store, you can’t even go to school, now you can’t go to the doctor?”

Debra Proctor was in another building on the hospital campus for an appointment when she heard police sirens.

“Police were everywhere in the parking lot, up and down the surrounding blocks,” said Proctor, a registered nurse for more than four decades. “They were still arriving when I was leaving.”

Kalen Davis, a lifelong Tulsa resident, was waiting in traffic around 5 p.m. local time when she saw multiple police cars responding to the scene.

In a video she shared with CNN, authorities can be seen running toward a building with their guns drawn. Two officers are seen taking long guns out of their trunks as more emergency vehicles race to the scene.

“I just knew that it was a shooting situation because I saw police running with rifles,” Davis, 45, told CNN. “That’s when I got emotional.”

Shooting occurred at town ‘sacred ground’

Saint Francis Health System, which runs the hospital, said in a statement that some offices will be closed for the remainder of the week.

Oklahoma state Rep. Melissa Provenzano, whose district includes the hospital, told CNN she was on campus the morning of the shooting and called it “the center of our community.”

“This is just one of the hallmark locations in our town,” she said, and credited hospital staff there for saving her father’s life when he contracted Covid-19.

“This campus is sacred ground for our community,” said Tulsa Mayor G.T. Bynum, who also expressed “profound gratitude” for the first responders who “did not hesitate today to respond to this act of violence.”

“The men and women of the Tulsa Police Department did not hesitate,” the mayor said.

Provenzano also hailed the effective police response yet urged more proactive work is needed to curb similar shootings in the future.

“I just can’t say enough good things about them,” she said of the police, “but you know, why were they needed in the first place?”

Pointing to gun accessibility and the need for “red flag” laws, she added, “We can do so much more here in Oklahoma to make these things preventable,” she said.