The deadliest mass shooting in America's history struck at Florida's very core early Sunday, killing 50 people in an Orlando nightclub minutes from the global hub of Disney World and in the name of the global terrorism group ISIS.

Omar Mateen, a 29-year-old Treasure Coast resident, registered Democrat, U.S. citizen, father and Indian River Community College graduate, was identified as the shooter.

More than 50 people also were wounded in the vicious 2 a.m. attack at the Pulse nightclub on Orange Avenue, where an estimated 300 club-goers scrambled to escape Mateen's shooting rampage.

Mateen, who bought the two guns used in the attack legally, according to federal officials, was shot dead by authorities who drove an armored vehicle through a wall of the club at about 5 a.m.

That was three hours after Mateen began shooting — a sound that club-goers initially thought was part of the revelry during the popular Latin theme night at the nightclub.

Janiel Gonzalez, 26, said he was signing his tab at the bar when the shots started. He initially thought they were fireworks.

>> Read more coverage of the Orlando nightclub shooting

“But it got louder and louder,” he said. “It wasn’t until everybody started smelling the ammunition everybody realized this is real life.”

Dozens of people dived to the floor and started climbing over each other looking for an exit. Many cut themselves crawling on the floor over glass from smashed beer bottles that were tossed by panicked patrons as the shooting started.

“I remember telling myself, ‘This is not how I die,’’’ Gonzalez said. “When I dropped to the floor and saw people crying and covered in blood, the scent of the ammunition and bullets, I was like ‘This is real life. This is happening right now.’”

Gonzalez said he never saw the gunman, who was in an adjacent room about 20 feet away.

Mateen, a registered security guard, had worked since 2007 for G4S, a worldwide firm which has its North American technology headquarters in Jupiter.

On Sunday, the company said in a statement it was “shocked” by the killings.

Yet Mateen was familiar to FBI agents who interviewed him at least twice since 2013.

FBI Special Agent in Charge Ronald Hopper said Mateen first came to the attention of authorities after making “inflammatory” comments to co-workers.

In 2014, Mateen was again investigated for potential ties to Mohammed Abu-Salha, 22, who went to the Middle East, trained, and returned to Vero Beach and Fort Pierce, to recruit.

The FBI says he didn’t recruit anyone, but it’s possible he did have contact with Mateen. Abu-Salha drove a truck bomb into a restaurant in Syria in 2014.

Mateen pledged allegiance to ISIS leader Abu Bakr al-Baghdadi in a 911 call he made during the shooting, and the ISIS said through the news organization Aamaq Agency that the Orlando attack was “carried out by an Islamic State fighter.”

Mateen attended prayers several times a week at the Islamic Center of Fort Pierce until just days before the shooting, said the mosque’s imam, Syed Shafeeq Rahman.

“I cried for all the people who died,” Rahman said Sunday. “Of course, it is a big shock for us.”

Rahman said he’s known Mateen since shortly after he took over as imam of the mosque in 2005 and that Mateen was usually with his 3-year-old son when he attended services.

Rahman said he has never spoken against homosexuality in his sermons.

“There is nothing outside the door that says you can’t come in and worship God and be here and pray if you are gay,” he said.

But Mateen’s father, Seddique Mateen, told NBC News that his son became angry earlier this year when he saw two men kissing on a Miami street.

“We are apologizing for the whole incident,” he said. “We weren’t aware of any action he was taking. We are in shock, like the whole country.”

The shooting prompted Gov. Rick Scott to declare a state of emergency for Orange County. The action eases the way for federal involvement in the case and allows for potential funding assistance.

“We are a strong and resilient state and we will devote every resource available to assist with the shooting in Orlando,” Scott said.

Gonzalez, the man at Pulse early Sunday, said his first thought was that the shooting was a hate crime.

Fearing Mateen was targeting gay men, he escaped the nightclub and hid in a women’s restroom at a nearby convenience store for 25 minutes.

It wasn’t easy getting out of the club. He said people were jumping over each other trying to get out. At one point, a man was inexplicably blocking a door, telling people to stay inside.

“As he is saying that, the shooter keeps getting closer and closer and the sound of the bullets is getting closer,” Gonzalez said. “Everyone starts to panic. People are getting trampled. ‘Let us out, let us out!’”

Mina Justice sat on a bench outside a nearby hospital and cried with her face in her hands. She had received a frantic phone call just after 2 a.m. from her son, Eddie, who was in the club when the shooting started. Minutes later she received a text.

“He texted her, ‘He’s got us hostage. I love you mommy,’” said Eddie’s cousin, Jeff Robinson.

That was the last contact Justice had with her son, Robinson said as of noon Sunday.

All day Sunday, people wandered down West Esther Street to the police barricade outside Pulse.

Some were curious onlookers, but others were desperate to find signs their loved ones were still alive.

Charlie Williamson was looking for a car owned by her friend K.J. Morris, a Pulse bouncer. Morris wasn’t answering or replying to calls and messages, but she couldn’t find Morris’ car – a potentially positive sign.

Iijima Brown showed up to look for her friend’s car, a Pulse patron whom she couldn’t reach on Sunday.

“It’s devastating,’’ Brown said as she wiped tears. “It’s one of those places where you don’t have anything like this happen.’’

Brown also said many gay bars in Orlando have security areas where patrons pass before entering. “They get wanded or patted down for weapons,’’ she said. “Pulse doesn’t do that.’’

The onlookers saw a steady procession of police officers. Workers from a fence company erected a chain-link fence around the building. The fence then was covered with a dark tarp, presumably for privacy once the bodies were taken out.

In Port St. Lucie late Sunday, the FBI searched a home at 519 Bayshore Blvd. associated with Mateen and his family.

As the investigation continues, residents “must not give in to blind rage and discrimination,” said Port St. Lucie Mayor Gregory Oravec, who has been mayor of the community of 180,000 since 2014. “People are asking how and why did this happen. In the face of this national tragedy, we have to be at our best.”