According to eyewitnesses, large numbers of dead bodies were seen carried out on stretchers and loaded into the back of nearby trucks and vans.
VIDEO: People helping to load up and transport Las Vegas shooting victims to the hospital
Latimes.com reports: Police also were investigating reports of a “suspicious device” down the street, outside the Luxor Hotel.
Concertgoers at a three-day Route 91 Harvest country music festival performance reported a burst of weapons fire as a Jason Aldean concert was underway. The shots appeared to be coming from an upper floor of the hotel, some witnesses said.
Video posted on social media showed a country artist mid-song at the open-air venue 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, said Aldean had been performing for about 20 minutes on the east side of Las Vegas Boulevard, across the street from Mandalay Bay, 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 and Sam Hunt and Jason 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.
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 being ordered to shelter in place.