The incident happened Sunday night at the Route 91 Harvest festival at the Mandalay Bay Hotel and Casino in Las Vegas. A gunman opened fire on concertgoers on the third night of the crowded music festival, killing at least 20 people and wounding around 100 more.

Jason Aldean, a country musician, was performing at the casino at the time of the incident when gunshots rang out, raining down on to the audience. Concertgoers panicked and screamed as they attempted to escape from the volley of gunshots from an automatic weapon.

Police receive reports of active shooter at Mandalay Bay

Las Vegas Metropolitan police initially tweeted to say they had received reports of an active shooter and asked people to avoid the area around the casino.

However later Joe Lombardo, the Clark County Sheriff, said in a media conference that more than 100 people had been shot, with at least 20 dead. However he said he is unable at present to give accurate figures and that the death toll could rise. Lombardo also added that off-duty police officers were among the victims.

SWAT team tracks down the gunman in the hotel

Multiple streets on the Strip were blocked by police as they searched the casino hotel for the gunman. A SWAT team eventually closed in on a room on the 32nd floor, where a possible suspect was thought to be located. Shortly before midnight, police confirmed the shooter was “down.” However Lombardo did say police are seeking a woman believed to have been traveling with the gunman by the name of Marilou Danley.

Aldean posted to Instagram some hours after the attack to let fans know he and his crew were unharmed and had left the stage safely.

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He said the evening’s incident had been “beyond horrific.” Jake Owens, an artist who opened for Aldean, said on Twitter that he had witnessed the incident and went on to warn his followers about the shooting and send his love to his daughter.

Witnesses speak about the Las Vegas shooting incident

Rick Messick was at the concert and told CBS News he witnessed the incident from the front row, saying he saw people lying in the parking lot with paramedics trying to stop the bleeding.

The Las Vegas Review Journal quotes Matt and Robyn Webb, visitors from Orange County, as saying they hid under their seats as the gunfire came in endless bursts from the Mandalay Bay Hotel. Robyn said the gunfire was “relentless.” When they finally moved across toward Reno Court, they saw at least 20 people lying bleeding in the streets, with Matt saying that was when they knew it was real.

Ivetta Saldana, another witness at the scene, said she was at the concert with a friend and that the gunshots initially sounded like fireworks.

However Aldean suddenly stopped singing and was rushed off the stage. Saldana said it was like a “horror show” – one minute people were standing around enjoying the concert and then next they were hitting the floor.