More than 50 people were killed in the worst mass shooting in modern American history when a lone gunman opened fire into an outdoor country music festival from the 32nd floor of a Las Vegas hotel on Sunday night, police said.

More than 200 people were injured as performer Jason Aldean was onstage, Sheriff Joseph Lombardo said at a news conference.

The gunman was identified by law enforcement officials as Stephen Paddock, 64, of Mesquite, Nevada.

Police responded to reports of the shooting just after 10 p.m. (1 a.m. ET), and the suspect was fatally shot in the Mandalay Bay Resort and Casion, officials said.

Authorities found several weapons in Paddock’s room after using explosives to enter, law enforcement officials reported. It was not immediately clear what kinds of weapons were found.

At least one off-duty Las Vegas police officer was shot, Lombardo said. Several other off-duty police officers are believed to be among the dead and injured.

Meghan Kearney described the chaotic scene.

“We heard what sounded like firecrackers going off. Then all of a sudden we heard what sounded like a machine gun. People started screaming that they were hit… When we started running out there were probably a couple hundred [people] on the ground,” she told MSNBC.

“People kept dropping and dropping. … People were getting shot one foot away from us,” she said. “People were trying to save their friends. There were gunshots everywhere. Helping them would’ve meant that we got shot, too.”

Police have located Paddock’s roommate, Marilou Danley, 62, for questioning, Lombardo said. They also found two vehicles related to the investigation: a Hyundai Tuscon and a Chrysler Pacifica Touring, both with Nevada license plates.

Earlier, police shut down the area and urged the public to stay away. Flights in and out of the airport were temporarily halted.

Aldean, who was named the Academy of Country Music’s Entertainer of the Year in April 2017, was on stage performing on the final night of the three-day Route 91 Harvest festival at the Las Vegas Village when the first shots rang out.

Aldean later said via Instagram that he and his band were safe.

Witnesses said that the first round of shots sounded like fireworks. Only after the second burst of gunfire did the band stop playing.

“After the second round… everybody hit the ground around us,” concert-goer Sean said on TODAY.

“It seemed like people were hit everywhere.”

Another concergoer, Jon Bessette, described a scene of “pandemonium” as “the band ran off stage.”

“Everyone was running, people were getting trampled,” he said.

Mandalay Bay tweeted out a statement that said, “Our thoughts & prayers are with the victims of last night’s tragic events. We’re grateful for the immediate actions of our first responders.”

Police urged families looking to locate missing loved ones to call 1-866-535-5654.

This is a developing story. Please check back for updates.

Richie Duchon and Andrew Blankstein reported from Los Angeles. F. Brinley Bruton, Rachel Elbaum and Yuliya Talmazan reported from London. Pete Williams reported from Washington.