At least 50 people were killed and multiple others were injured in a shooting near the Mandalay Bay Resort and Casino in Las Vegas on Sunday, police said.

It is the deadliest mass shooting in US history, with the death toll surpassing the 49 killed at a nightclub in Orlando in June 2016.

As ambulances and other first responders swarmed in to help, the gleaming Las Vegas strip shut down. Tourists hid in their hotel rooms. Flights headed into the McCarran International Airport airport were held elsewhere.

As bursts of gunfire crackled in the air, people outside of the casino ducked and screamed.

“We’re going to get trampled if we don’t go,” a bystander could be heard saying in a dramatic video of the incident. Confusion appeared to abound as those outside fled the scene with another person saying “it’s fireworks.”

One witness, Jake Freeman, said he was standing on the rooftop of a nearby hotel when the shooting broke out.

“I had a bird’s-eye view” of the shooting, Freeman said in a phone interview with ABC News. He said he saw “crowds of people running” as people “dropped to the ground.”

“At the moment we didn’t realize that they were being shot,” he said.

Officials at the University Medical Center in Las Vegas told ABC News that it had at least 20 victims with gunshot wounds, with the number expected to grow. The hospital did not provide information on the victims’ conditions.

“Please avoid heading to the south end of the Strip,” the department said in a Twitter post early Monday. “Las Vegas Blvd is shut down at Tropicana, southbound past Russell Rd at this time.”

The police reported clearing out the Mandalay Bay’s 29th floor and working their way up to the 32nd floor. A police Twitter post described reports of an “active shooter” near or around the Mandalay Bay casino.

Several SWAT teams were sent to the hotel, and officers reported being pinned down by gunfire, according to emergency radio traffic. Shortly before midnight the Las Vegas Police Metropolitan Police Department reported that “one suspect is down,” and soon thereafter the police said they did not believe there were any more active gunmen.

In the confusion after the shooting, the police also descended on the Ali Baba Restaurant, about a 10-minute drive from the Mandalay Bay, and they also investigated reports of a shooting at the New York-New York Hotel and Casino.

UPDATE:

The suspected gunman in the mass shooting at a music festival in Las Vegas has been named as 64-year-old Stephen Paddock.

Witnesses described seeing flashes of light high up in the tower. The shooter was believed to have been shooting down at crowds of concert-goers from the 32nd floor of the of the Mandalay Bay Hotel.

Announcing the suspect’s name, Las Vegas Sheriff Joseph Lombardo said police had “located numerous firearms” in Paddock’s hotel room.

A SWAT team used a controlled explosion to enter the hotel room, where they shot the suspect dead.

Stephen Craig Paddock, 64, has lived on Babbling Brook Court in Mesquite, Nevada, since June 2016. He previously lived in Reno, Nevada, from 2011 to 2016, and also had an address in Melbourne, Florida, from 2013 to 2015. He has also lived in Henderson, Nevada, and several locations in California since 1990. He was born April 9, 1953.

Sheriff Joe Lombardo, when asked by a reporter if it was an “act of terrorism,” said “no, not at this point. We believe it was a local individual. He resides here locally. I’m not at liberty to give you his place of residence yet, because it’s an ongoing investigation, we don’t know what his belief system was at this time. … Right now we believe he is the sole aggressor at this point and the scene is static.”