Orlando Police described it as a “mass casualty situation”, and said “multiple people are dead" and are still inside the club.
Orlando Police Chief John Mina said “approximately” 20 were dead inside the nightclub in the city, but the exact number of casualties not yet known.
The FBI are on the scene and police confirmed “every source in the FBI would be brought to bear”, as they would be investigating the shooting as an act of terrorism.
The shooter’s identity is still unknown, and it is unclear if he has links to international terror groups like Islamic State or if he was a lone wolf.
But police confirmed he is not f-rom the local area. They are searching his home for any more devices and clues. He has been described as “organised” and “well-prepared”.
After the shooting occurred at 2am local time, a police officer engaged the shooter in gunfire, when he appeared to be carrying an assault-type rifle and handgun.
At 5am local time, a SWAT team made the call to rescue the hostages inside the club.
Police did find a “suspicious device” on the shooter, which is consistent with earlier reports he was carrying a bomb on him. But they have been unable to find any other devices so far.
The popular gay dance club issued a Facebook status up-date of: “Everyone get out of pulse and keep running” after the shooting first occurred.
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, 2am, 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 whe-re only workers are allowed. People inside were able to then escape through the back of the club.
First responders crowd around victims f-rom a mass shooting at an Orlando nightclub. Picture: Anthony Torres via FacebookSource:Facebook
Mina Justice was outside the club 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.”
Orlando Police officers direct family members away f-rom a multiple shooting at a nightclub in Orlando. Picture: APSource:AP
Multiple emergency vehicles including the Orlando Fire Department’s bomb squad and hazardous material team went to the scene. Local streets were cordoned off.
Members of the public have been told to stay away f-rom the area by Orlando Police.
Speaking to Sky News, clubber Ricardo Negron, who was inside when the shooting began, described how the gunman raked the club with bullets.
Pulse nightclub whe-re a shooting has occurred in Orlando, Florida. Picture: SuppliedSource:Supplied
“At around 2am someone started shooting. People just d-ropped on the floor. I guess the shooter was shooting at the ceiling because you could see all the glass f-rom the lamps falling,” he told the network.
He described hearing “non-stop firing” which probably lasted less than a minute but felt like a lot longer.
“There was a brief pause in the shooting and some of us just got up and ran out the back.” “People have definitely been injured — or worse.”
It was not immediately clear how many people were inside the club when the shooting began.
Another clubber called Christopher Hanson told CNN he heard “loud banging noises, like gunshots going off.” He said at first he thought it may have been the music “until you heard too many shots. It was like, bang, bang, bang, bang.”
Jermaine Towns, left, and Brandon Shuford wait down the street f-rom a multiple shooting at the nightclub. Towns said his brother was in the club at the time. Picture: APSource:AP
“I didn’t see any of the actual shooters. I just saw bodies going down,” he told CNN, saying he was ordering a drink at the bar at the time.
“I fell down. I crawled out. People were trying to escape out the back. I just know that when I hit the ground, I was crawling and I hit my elbows and my knees. When I got across the street, there were people -- blood everywhe-re,” he said.
Those who were inside or near the nightclub have described their shock and posted videos of the crime scene on social media.
The incident came just two days after a deadly shooting at the nearby Plaza Live Theater in which a heavily-armed gunman shot and critically wounded singer Christina Grimmie, a former contestant on the popular TV talent show “The Voice”.
She was rushed to hospital but died of her wounds.
The theater is located less than four miles away f-rom Pulse nightclub. The gunman, 27-year-old Kevin James Loibl, then killed himself. He was found to be armed with two handguns, ammunition and a hunting knife, police said. His motive remains unknown.
Orlando Police said the shooting death of Ms Grimmie was not linked to the shooting at Pulse nightclub.