FINAL UPDATE: Police now say they have located a woman wanted for questioning after a mass shooting in Las Vegas left more than 50 people dead (and more than 400 injured):

UPDATE 5 [6:26 a.m. Eastern]: NBC News has now identified the gunman in a mass shooting on the Las Vegas strip Sunday night at the Route 91 Harvest Festival — in which police now say more than 50 people died, including two off-duty police officers, and more than 200 were injured — as 64-year-old Stephen Paddock.

Clark County Sheriff Joseph Lombardo told the media that authorities confronted the alleged shooter on the 32nd floor of the Mandalay Bay Casino, and that the man ‘died.’ NBC and other sources say law enforcement is still looking for Marilou Danley — variously described as the suspect’s “companion” or the woman under whose name the hotel room had been rented — who is said to have been traveling with Paddock.

UPDATE 4 [4:40 a.m. Eastern]: Authorities now say at least 20 people were killed and more than 100 injured — dozens critically — after what they believe to be a lone gunman opened fire using fully automatic weapons on a crowd gathered for a country music festival late Sunday night in Las Vegas.

Reports indicate the shooter fired from an elevated vantage point on the 32nd floor of the Mandalay Bay Casino. Police reported the shooter ‘down,’ though preliminary and wholly unconfirmed information suggested the gunman had taken his own life.

UPDATE 3 [4:07 a.m. Eastern]: CNN reports Las Vegas police and law enforcement are not looking for a second shooter after ‘downing’ one suspect, although an investigation is active and ongoing. Initial confusion and chaos as the news of a mass shooting on the Strip at a concert indicated the possibility of multiple locations and potentially multiple shooters — though neither was confirmed and police now contest the latter.

Thus far, two people are confirmed dead and at least 24 were injured — all by gunfire believed to have been fully automatic — although those preliminary figures are expected tragically to climb.

UPDATE 2 [3:20 a.m. Eastern]: The Las Vegas Metro Police Department has confirmed one shooter is down, but the situation remains open and under active investigation.

“Confirming that one suspect is down. This is an active investigation. Again, please do not head down to the Strip at this time,” LVMPD tweeted.

Statements from witnesses are beginning to circulate.

“There was blood everywhere,” one eyewitness to the shooting said.

“People were hit within 20 feet of us,” described concertgoer, Rick Messick, to CBS2. “There were several people laying in the parking lot … they were trying to stop the bleeding.”

UPDATE 1 [3:01 a.m. Eastern]: RT is reporting authorities have confirmed two dead in the mass shooting in Las Vegas, with 24 injured — though reports from social media and witness video and testimony from the scene intimates those numbers may climb significantly.

An apparent mass shooting has taken place in Las Vegas, when a gunman opened fire on crowds attending the Harvest Country Music Festival outside the Mandalay Bay Casino — although details remain sketchy at this time, as law enforcement and first responders are still arriving on scene.

Law enforcement is treating the situation as a ‘mass casualty incident’ — and though it has been confirmed multiple people were transported to the hospital — the extent of injuries and almost certain death toll remain unknown at this time.

“We’re investigating reports of an active shooter near/around Mandalay Bay Casino. Asking everyone to please avoid the area. #LVMPDnews,” Las Vegas Metro Police Department stated on Twitter.

Police are urging people to stay far away from the area — including major highways nearby — as they and emergency medical personnel must have access open.

According to at least one witness, speaking to KTNV, described the gunfire sounding like “just pops, just little pops — as if fireworks had gone off.”

KTNV reports the gunfire began toward the end of a performance by Jason Aldeen at a country music festival. Cell phone video indeed shows crowds stunned by a sudden outburst of rapid, reverberating gunfire — and then running desperately for safety once they realized what was happening.

“Holy f–k this girl just got shot in the f–king head,” Professional poker player and Instagram star, Dan Bilzerian — who was attending the concert — wrote on Instagram, as cited by the New York Post.

Authorities have shut down portions of the storied Strip until the situation is fully under control. Also, Las Vegas-McCarran International Airport is now diverting flights and has closed pending the same.

At the time this article is published, the number of gunmen, victims, and the exact extent of the obvious tragedy remain unknown.

This article will be updated as information becomes available.