UPDATED: The Islamic State has taken credit for the nation's deadliest mass shooting in Orlando which left 50 people dead and over 50 injured.
"The armed attack that targeted a gay night club in the city of Orlando in the American state of Florida which left over 100 people dead or injured was carried out by an Islamic State fighter," the Islamic State's news agency Amaq said, according to Reuters.
City officials identified Omar Mateen, 29, from Port St. Lucie, as the killer of 49 people early Sunday inside Pulse, a gay nightclub in Orlando.
It is the deadliest mass shooting in U.S. history.
FBI agent Ron Hopper said investigators had “suggestions that individual has leanings towards” radical Islamic terrorism, but a motive was not yet clear. Mateen called 911 moments before the attack and pledged his allegiance to Islamic State, a federal law enforcement official said.
At least 53 more people were injured, Orlando police said. Police shot and killed the gunman.
The earliest reports claimed 20 people had died and 42 were injured in the 3 a.m. shooting.
"It's appears he was organized and well-prepared," Orlando police chief John Mina said, adding that the shooter had an assault-type weapon, a handgun and "some type of (other) device on him." He was also carrying a suspicious device, possibly a suicide vest, when he opened fire on the dance floor.
"There's blood everywhere," U.S. Rep. Alan Grayson told reporters. "There's an enormous amount of evidence to be collected."
Gov. Rick Scott arrived in Orlando Sunday afternoon to meet with law enforcement and local officials.
“Our thoughts and prayers are with the victims, families and all those affected by this horrific tragedy," Scott said. "We are a strong and resilient state and we will devote every resource available to assist with the shooting in Orlando. Our state emergency operations center is also monitoring this tragic incident. I have been in constant communication with Orlando Mayor Buddy Dyer, Orange County Mayor Teresa Jacobs and state and local law enforcement this morning. I would like to also thank all the first responders who quickly came to assist and help those in need.”
Early Sunday afternoon, Scott declared a state of emergency in Orange County.
President Barack Obama called the shooting an "act of terror and an act of hate."
"In the face of hate and violence, we will love one another," he said Sunday afternoon. "We will not give into fear."
Thousands flocked to blood banks to donate blood to the victims, with many Orlando-area blood banks at capacity.
As of this article's writing, there was no clear motive, but Assistant Special Agent in Charge Alcohol, Tobacco and Firearms Tampa Field Division Trevor Velinor said the gunman legally purchased the firearm in Florida last week.
Rasha Mubarak, Orlando regional coordinator of the Florida affiliate of Cair, America's largest Muslim civil liberties and advocacy organization, issued a statement of condemnation for the nightclub shooting.
"We condemn this monstrous attack and offer our heartfelt condolences to the families and loved ones of all those killed or injured," Mubarak said. "The Muslim community joins our fellow Americans in repudiating anyone or any group that would claim to justify or excuse such an appalling act of violence."
At least nine officers were involved in the shootout, Mina said. Several coroner vans were seen traveling toward the nightclub.
"So, terrorism has finally come to Florida," one distraught onlooker told CNN. "It feels like it came looking for me. I take it personally," he said. "I have friends in that club or in the hospital, I don't know where they are right now, I can't get them to answer their phones."
After authorities heard by cellphone from victims inside the club who said they were wounded and in danger, the nine officers stormed in to confront Mateen. One officer suffered an eye injury, and officials credited his helmet for saving his life.
Witnesses described a bloody scene in and around the downtown club, with dozens of shots fired.
Police said an off-duty officer working a security job at the club was the first to exchange gunfire with the attacker, who then barricaded himself inside the club and took hostages.
Witnesses said authorities seemed to be searching for someone in the area around the club after there were reports that there was a second shooter involved in the attack. But authorities said those accounts were unfounded.
Although the club was preparing to close about the time the assault began, some 320 people were still inside.
One person who said he had been at the club when the shooting began managed to escape because he was near an exit. Other people who were dancing or at the bar tried to take cover by dropping to the floor.
One witness told the Orlando Sentinel that the shooting lasted “the duration of an entire song.”
Another clubgoer, Jon Alamo, said he was at the back of one of the club’s rooms when the gunman came in through the front.
“I heard 20, 40, 50 shots,” he said. “The music stopped.”
Mina Justice told CNN she was outside the club trying to contact her 30-year-old son, 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.”
Video of emergency crews helping victims was posted on social media as other victims were carried or were walking to nearby Orlando Regional Medical Center. But the New York Daily News also reported emergency services were so overwhelmed the wounded were being loaded on the back of pickups to be transported.
Soon after police reported that the gunman had been found dead, the club posted online: “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.”
Update: Orlando police have identified 36 of the 49 victims whose next of kin have been notified. To see the full list, click here.
(This report was taken from a variety of newspaper and television network news sources. It is a rapidly developing story and may be further updated. Please check back.)