LAS VEGAS — More than 20 people were killed and at least 100 others injured after a gunman opened fire Sunday night at a country music festival opposite the Mandalay Bay hotel and resort on the Las Vegas Strip, authorities said.
University Medical Center spokeswoman Danita Cohen said the hospital is still evaluating the condition of "many patients" with gunshot wounds in the wake of the shooting, but at least 14 were in critical condition.
Police reported that the suspect, a Las Vegas resident, was dead.
"Right now we believe it's a solo act, a lone wolf attacker," Las Vegas Metropolitan Police Sheriff Joe Lombardo said.
He said authorities were seeking to interview a woman who was believed to have been traveling with the suspect, a resident of Las Vegas whose name was not immediately released.
Two of the dead may include a pair of off-duty police officers who were attending the concert, Lombardo said.
Authorities established a command post and triage center, and shut down parts of the Strip.
Police investigated reports of a "suspicious device" down the street, outside the Luxor Hotel, but there were no reports that it was involved in an attack.
A three-day Route 91 Harvest country music festival performance was underway across Las Vegas Boulevard from the Mandalay Bay hotel when the shooting erupted. Concertgoers reported a burst of weapons fire as a Jason Aldean performance was underway.
The shots appeared to be coming from an upper floor of the hotel, some witnesses said.
Video posted on social media showed the open-air concert fully underway when bursts of automatic gunfire rang out in rapid succession. Dozens of concertgoers dropped to the ground, screaming, while others ran, some in pairs or in groups with their arms linked.
The shooting went on for about more than 30 seconds before the music stopped, and another burst was heard later.
"Get down, stay down," one woman shouted. "Let's go," another voice said. Another wave of gunshots followed soon after.
Seth Bayles, of West Hollywood, Calif., said Aldean had been performing for about 20 minutes when he heard shots.
"I thought it was like bottle rockets going off," Bayles said. "Then we saw people dropping. We saw someone get hit and then we started running."
Bayles said he was probably 50 feet from the stage when he heard the shots. "We saw people down all over the place."
Bayles said Aldean was quickly pulled off stage, and soon after, the band was brought off as well.
Two men near the casino said they heard a helicopter with a bullhorn yelling "Go! Go! Go!" as the incident unfolded. Others said they saw police and SWAT teams streaming into the Mandalay Bay casino.
Bernice Allard, who came to the concert with her husband, Frank Allard, said there was screaming when the shooting began. "Single shot. Single shot, then a lot of shots," Frank Allard said.
Allard, 56, said he had come to see Eric Church, Sam Hunt and Aldean, who was into his fourth or fifth song when the shooting began. He said the crowd began to stampede, and he grabbed a nearby fence, stretched both arms wide and tried to shield his wife from the danger. Then they ran.
"We followed the crowd out," Bernice Allard said.
Alarm spread up and down the strip as news of the shootings spread.
Alfonzo Ewing had arrived for the overnight shift as a cook at the White Castle at the Best Western Plus Casino Royale on the northern side of the strip, a little more than two miles from Mandalay Bay.
"We heard reports of gunshots and customers rushed to jump the counter for safety. Everyone just took off running from the White Castle and the hotel," said Ewing, 37. "Employees and customers went downstairs to hide in the break room. We're here now, 15 of us, with customers. We're safe but we don't know what's happening."
Kevin Daly, 58, of Long Beach, Calif., said he had been playing pai gow at the MGM Grand hotel, down the street from the concert venue, and left to see if he could play a Game of Thrones game near the entry when chaos erupted.
"All these people started running and screaming, and then that stopped for about a minute, and then more people started coming in the other way and ran through where I was," he said. "There were so many people walking and running and people crying and people saying there's an active shooter on the street, so I finally asked one of the waitresses what's going on and she said the shooter is outside of the casino."
Daly said the entire area was put on lockdown so he went upstairs to his room. "Out the windows, we can see Mandalay Bay, we can see all the police cars and all the lights and there are helicopters all over the place."
Officials at McCarran International Airport reported that some flights have been diverted in the wake of the shootings. "Expect delays," the airport said on Twitter.
Hospital personnel across Las Vegas have been paged to work, local media reported.
Parts of I-15 near the Strip were also shut down, and hotel guests across the Strip were ordered to shelter in place.
Aldean was the final act of the Route 91 Harvest festival, while dozens of others had played over the course of the weekend, including Church, Hunt and Maren Morris. In numerous tweets, artists communicated with fans and followers, expressing their sorrow and prayers for anyone injured and telling loved ones that they were safe.
Jake Owen, who played the main stage before Aldean, tweeted: "Praying for everyone here in Vegas. I witnessed the most unimaginable event tonight. We are okay. Others aren't. Please pray."
(Montero reported from Las Vegas and Tchekmedyian from Los Angeles. Times staff writers Jaweed Kaleem, Seema Mehta and Jevon Phillips in Los Angeles and Rong Gong Lin II in San Francisco contributed.)