On Monday evening in Manhattan, a mass shooting unfolded inside the 44-story skyscraper at 345 Park Avenue, which houses both the NFL’s headquarters and major financial firms including Blackstone and KPMG. The New York Post reports, according to authorities, 27-year-old Shane Tamura of Las Vegas entered the building around 6:30 p.m., armed with an AR-15 style rifle. He opened fire in the lobby and on upper floors, causing widespread panic and chaos among employees and visitors.

Witnesses described a barrage of rapid gunfire and frantic scenes, as people scrambled for cover and emergency alerts ordered those inside to shelter in place. Law enforcement responded swiftly, cordoning off surrounding streets and conducting floor-by-floor searches as the situation remained fluid inside the tower.

One witness, Nekeisha Lewis, who was having dinner in the plaza told NBC News that she clearly heard the shots then saw the “first wall of the first floor shatter.” The witness then said she realized it was a shootout and a victim approached Lewis and her partner who both noticed the man was wounded. The victim yelled to them “Help! Help! I’ve been shot!” Lewis said the police immediately tended to the victim. The people around her realized what was happening due to the heavy rounds of fire they heard, Lewis added.

Another witness who did not report hearing the gunfire said that they knew what was going on because of social media, then they heard authorities direct them to “get away from the windows.”

According to The Post, Jessica Chen, who was on the second floor of the 44-story building, told ABC News, “‘We heard multiple shots go off in quick succession from the first floor, and a lot of us just rushed into the room.’ Chen told the outlet that she and about 150 other people were in the middle of a presentation when the gunfire started — sparking panic.”

“Some went out in the back door, out onto the street,” Chen added. “Other people, including me, we ran into the conference room and then eventually barricaded the tables across the doors and just stayed still.”

Another man—reportedly present in the tower’s lobby when the gunman entered and opened fire—ended up struggling to breathe on the steps of a nearby office building as he phoned a loved one to recount what had happened.

“I was at work, and this guy came in with an assault rifle and started shooting. I was in the lobby at work,” the man said while on his phone.

“He buried his face in his hands as he gasped for breath, and had a bandage on his knee and on a hand as a police officer tended to him,” The Post reports.

At least five people were reported killed, including an off-duty police officer working as a security guard, and at least six others were injured. Tamura ultimately barricaded himself inside the building, where he reportedly took his own life. Authorities suspect Tamura acted alone. In the aftermath, NYPD, FDNY, and FBI were on the scene, and the building remained locked down as investigations continued.