Worst Mass Shooting in US History Called 'Domestic Terror Incident'

A gunman who federal authorities say had possible ties to terrorism opened fire early Sunday morning at a packed Orlando nightclub, killing 50 people and wounding at least 53 more in a bloody scene that ended hours later when police stormed the building and killed the shooter.

"This is an incident ... that we certainly classify as a domestic terror incident," Orange County Sheriff Jerry Demings said at the press conference held Sunday morning, according to The Washington Post.

The gunman was identified as Omar Mateen, Rep. Alan Grayson said during the press conference. Mateen was a U.S. citizen, Grayson said, though that was "not true of other family members of his." Mateen, 29, lived in Fort Pierce, Fla. He was born in the U.S. to parents of Afghan origin and was a Muslim, Fox News confirmed.

Orlando Mayor Buddy Dyer asked Gov. Rick Scott to declare a state of emergency following the attack, which is the worst mass shooting in U.S. history. Before today, the most deadly domestic shooting happened on April 16, 2007, at Virginia Tech in Blacksburg, Va. A lone gunman, Virginia Tech student Seung-Hui Cho, killed 32 people before killing himself.

Authorities were going through Mateen's belongings on Sunday morning trying to identify a motive for the attack, Grayson said.

"More likely than not that it was an ideologically motivated attack," Grayson said, though he said it was unclear if Mateen was linked to any terror groups.

"It's not coincidence the attack took place where it did and when it did," Grayson said.

The shooting in Orlando at Pulse, which bills itself as "the hottest gay bar" in the city and was packed with more than 300 people, was reported minutes after 2 a.m. Sunday. In addition to those killed inside the club, at least 42 people were taken to area hospitals. Dozens of party-goers remained hostages in the club for several hours after the initial shooting, prompting SWAT teams to pour inside. Shortly after 6 a.m. local time, Orlando police tweeted that the gunman had been killed.

The shooter was "trained in the use of weapons," Rep. Peter King told CNN, though King didn't elaborate on what type of training that was.

The incident "is being investigated as an act of terrorism," said Danny Banks, special agent in charge at the Florida Department of Law Enforcement.

Banks said the suspected shooter - who was armed with an "assault-type rifle" and a handgun -- was killed at about 5 a.m. in a shootout with SWAT team officers who were called in "to rescue hostages," Chief John Mina of the Orlando Police Department said.

Mina said officers were engaged in a gun battle outside the club before the suspect went back into the building, where more shots were fired. He said the gunman then took several hostages.

"It appears he was organized and well-prepared," the chief said, adding that the shooter had an assault-type weapon, a handgun and "some type of (other) device on him."

At least 9 officers were involved in raiding the nightclub, and one officer was injured, according to Banks. The injured officer was hit by a bullet and his Kevlar helmet saved his life, Banks said.

Orlando Mayor Buddy Dyer credited law enforcement with saving more lives by their heroic efforts.

"Many were saved by the heroic efforts of the Orlando Police Department and Orange County Sheriff's Office," he said.

Witnesses in the club reported mass chaos after hearing several shots ring out inside the nightclub.

Pulse Orlando posted on its own Facebook page around 2 a.m.: "Everyone get out of pulse and keep running." Just before 6 a.m., the club posted an update: "As soon as we have any information we will update everyone. Please keep everyone in your prayers as we work through this tragic event. Thank you for your thoughts and love."

Mina Justice was outside the club early Sunday trying to contact her 30-year-old son Eddie, who texted her when the shooting happened and asked her to call police. He told her he ran into a bathroom with other club patrons to hide. He then texted her: "He's coming."

"The next text said: 'He has us, and he's in here with us,'" she said. "That was the last conversation."

Jon Alamo said he was at the back of one of the club's rooms when a man holding a weapon came into the front of the room.

"I heard 20, 40, 50 shots," Alamo said. "The music stopped."

Club-goer Rob Rick said it happened around, 2 a.m., just before closing time.

"Everybody was drinking their last sip," he said.

He estimated more than 100 people were still inside when he heard shots, got on the ground and crawled toward a DJ booth. A bouncer knocked down a partition between the club area and an area in the back where only workers are allowed. People inside were able to then escape through the back of the club.

Christopher Hansen said he was in the VIP lounge when he started hearing gunshots. He continued to hear shooting even after he emerged, where police were telling people to back away from the club. He saw injured people being tended to across the street.

"I was thinking, are you kidding me? So I just dropped down. I just said please, please, please, I want to make it out," he said. "And when I did, I saw people shot. I saw blood. You hope and pray you don't get shot."

Ricardo Negron Almodovar, who posted a message on the club's Facebook page describing his harrowing escape after shots broke out, described a chaotic scene.

"People on the dance floor and bar got down on the floor and some of us who were near the bar and back exit managed to go out through the outdoor area and just ran," he posted on the club's Facebook page.

"I am safely home and hoping everyone gets home safely as well."

Police said there was no more threat to the area.

Fox News' Chad Pergram and The Associated Press contributed to this report.

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Editor's Note: This story was updated at 11:50 a.m. ET on June 12, 2016.