At least four people were killed Wednesday in a shooting on a hospital campus in Tulsa, Oklahoma, police said in a news conference Wednesday evening.

"It was just madness inside, with hundreds of rooms and hundreds of people trying to get out of the building," Meulenberg told CNN Wednesday night.

President Joe Biden has been briefed on the shooting, a White House official said. The White House is closely monitoring the situation and has reached out to state and local officials to offer support.

"What happened today in Tulsa is a senseless act of violence and hatred," Oklahoma Gov. Kevin Stitt wrote on Twitter. "I am grateful for the quick and brave actions of the Tulsa Police Department and other first responders who did their best to contain a terrible situation."

The Warren Clinic Orthopedic offices in the Natalie Building will be closed for the balance of the week," the system wrote.

"Police were everywhere in the parking lot, up and down the surrounding blocks," Proctor said. "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.

"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."