ORLANDO: Orlando police officers wait outside of Pulse nightclub after a fatal shooting and hostage situation yesterday in Orlando, Florida. – AFP

ORLANDO, Fla: A gunman killed 50 people at a packed gay nightclub in Orlando, Florida yesterday in the worst mass shooting in US history which authorities described as a possible act of terrorism. Police killed the shooter, who was identified as Omar S Mateen, a Florida resident. A top US congressman said Mateen may have pledged allegiance to the Islamic State militant group. US officials cautioned, however, that they had no immediate evidence of any direct connection with Islamic State or any other foreign extremist group.

Mateen called 911 before the shooting and swore allegiance to Islamic State, NBC News said on Twitter. In a posting on its website, MSNBC said Mateen swore allegiance to Islamic State leader Abu Bakr Al-Baghdadi.

Fifty-three people were wounded in the rampage, which Orlando Mayor Buddy Dyer said was the deadliest single US  shooting incident, eclipsing the 32 people killed in the 2007 massacre at Virginia Tech university. "Today we're dealing with something that we never imagined and is unimaginable," Dyer said, more than doubling an earlier estimate that about 20 bodies had been found.

A police officer working as a security guard inside the Pulse nightclub, which has operated in downtown Orlando since 2004 and was hosting some 350 revelers, exchanged fire with the suspect at about 2 am (0600 GMT), police officials said.

"Everyone get out of pulse and keep running," the club's management wrote on Facebook as the incident unfolded. A hostage situation developed, and three hours later SWAT team officers used armored cars to storm the club before shooting dead the gunman. It was unclear when the victims were killed.

Dozens of terrified patrons, some of whom had been hiding in restrooms, were rescued. One officer was injured when he was hit in his helmet while exchanging fire with the gunman, police said. Representative Adam Schiff, the top Democrat on a congressional intelligence committee, noted that the shooting took place during Ramadan, and that ISIS leaders in Syria have urged attacks during this time. "The target was an LGBT nightclub during Pride, and - if accurate - that according to local law enforcement the shooter declared his allegiance to ISIS, (that) indicates an ISIS-inspired act of terrorism," Schiff said in a statement.

'DIFFERENT KIND OF CASE'

If confirmed as an act of terrorism, it would stand as the deadliest such attack on US soil since Sept 11, 2001, when Al-Qaeda-trained hijackers crashed jetliners into New York's World Trade Center, the Pentagon and a field in Pennsylvania, killing some 3,000 people.

A pair of ethnic Chechen brothers killed three people and injured more than 260 with a pair of homemade pressure-cooker bombs at the Boston Marathon in April 2013. Asked if the FBI suspected the gunman might have had inclinations toward militant Islam, including a possible sympathy for Islamic State, Ronald Hopper, an assistant FBI agent in charge, told reporters: "We do have suggestions that the individual may have leanings toward that particular ideology. But right now we can't say definitively."

US Senator Marco Rubio of Florida, who sits on the Senate intelligence and foreign relations committees, told CNN he understood that the gunman had worked for a security company and so would have undergone some background checks. "Over the next couple of days they're going to be looking to see where this individual was inspired to carry out this horrifying act of terrorism," Rubio said. "I think we're going to be talking about a very different kind of case here soon."

President Barack Obama ordered the federal government to provide any assistance needed to Florida police investigating the shooting, the White House said. He was due to speak later yesterday. The attacker was carrying an assault rifle and a handgun, Orange County Sheriff Jerry Demings said. He was also carrying an unidentified "device", Orlando Police Chief John Mina said earlier.

Video footage showed police officers and civilians carrying some people away from the club and bending over others on the ground. Dozens of police cruisers, ambulances and other emergency vehicles could be seen in the area.

'HORRIFIC ACT'

"It's definitely a tragedy not only for the city but for our entire nation," Mina told reporters. "We believe this is a tragedy that could happen anywhere in the United States of America, and what we need to do is continue to be vigilant." Pulse, which was crowded for a Latin music night, describes itself on its website as more than "just another gay club." One of the founders and owners, Barbara Poma, opened it more than a decade ago in an effort to keep alive the spirit of her brother, who died after battling HIV.

The choice of target was especially heart-wrenching for members of the US lesbian, gay, bisexual and transgender community, LGBT advocacy group Equality Florida said in a statement. "Gay clubs hold a significant place in LGBTQ history. They were often the only safe gathering place and this horrific act strikes directly at our sense of safety," the group said.  "We will await the details in tears of sadness and anger."

Orlando has a population of 270,930 and is the home of the famed Disney World amusement park and many other tourist attractions that attracted 62 million visitors in 2014. It was the second deadly shooting at an Orlando night spot in as many nights. Late Friday, a man thought to be a deranged fan fatally shot singer Christina Grimmie, a former contestant on "The Voice", as she was signing autographs after a concert.

FBI agent Ron Hopper said there was no further threat to Orlando or the surrounding area.  When asked if the gunman had a connection to radical Islamic terrorism, Hopper said authorities had "suggestions that individual has leanings towards that." Police had said previously on Twitter that there was a "controlled explosion" at the scene of the shooting. Mina said that noise was caused by a device intended to distract the shooter.

A woman who was outside the dance club early yesterday was 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,'" Mina Justice said. "That was the last conversation." Dozens of police vehicles swarmed the area around the club. At least two police pickup trucks were seen taking what appeared to be shooting victims to the Orlando Regional Medical Center.

Pulse posted on its own Facebook page around 2 am: "Everyone get out of pulse and keep running." Just before 6 am, 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."  Local, state and federal agencies were investigating.

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."

BEFORE CLOSING TIME

Club-goer Rob Rick said the shooting started 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 heard gunshots. He continued to hear shooting even after he emerged and police urged people to back away from the club. He saw the wounded 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." - Agencies