The gunman, identified by law enforcement officials as Omar Siddiqui Mateen, entered Pulse, a popular gay dance club in downtown Orlando, just after 2:00am and began shooting patrons using an AR-15-style assault rifle and a handgun. He then took hostages and remained in a standoff with police unit they stormed the club at around 5:00am and killed him in a gun battle. Pulse was crowded with some 350 revelers on a Latin music night when the attack happened.A lengthy exchange of gunfire could be heard from outside the club in one video posted on Twitter at 5:40am.Related: What We Know So Far About Omar Siddiqui Mateen, the Orlando Nightclub Gunman
"At first we thought it was the DJ adding shots into the set-list… and when we realized it was something different people were just ducking and screaming," said Luis Burbano, a witness who told ABC News he was bartending at the club last night when the shooting started. "The gunshots got closer… there was a break after 10 to 20 gunshots… and we started jetting up an exit towards the stage, and then the shooting started again, and they were getting louder.""I heard at least 20 to 30 rounds by the time I got out," Burbano said.Gunfire exchanged at — Nic Hornstein (@nichornstein)June 12, 2016
Joshua McGill, who was at the club when the shooting started, described how he fled the attack in a post on Facebook.Related: How Trump, Clinton, and Other US Politicians Reacted to the Orlando Attack
No police officers were seriously injured in the raid on the club, but one was hit in the helmet with a bullet.Walking to ORMC now. I'm ok. Friend got shot. I've never seen so much blood and mayhem or been so scared ever. — John PA (@lakecitymedman)June 12, 2016
NBC News reported that several unnamed law enforcement officials said Mateen pledged allegiance the Islamic State group in a call to 911 before the attack.Ron Hopper, the FBI agent overseeing the agency's Tampa field division, told reporters that Mateen made a call to 911 early Sunday morning that was "general to the islamic State," but said he hadn't heard the tape and couldn't confirm that Mateen had pledged allegiance to the militant group in the call.Pulse shooting: In hail of gunfire in which suspect was killed, OPD officer was hit. Kevlar helmet saved his life. — Orlando Police (@OrlandoPolice)June 12, 2016
Hopper also said the FBI had interviewed Mateen at least three times in the past five years about suspected terrorist connections, but he was not under surveillance or investigation at the time of Sunday's attack. He also said Mateen legally purchased at least two of the weapons used in the attack in the past week.Related: President Obama Says Florida Nightclub Shooting is an 'Act of Terrorism'
It's still unclear whether the Islamic State supported Mateen, encouraged him to mount the attack, or if the group was even in direct contact with him.Mateen was born in the US in 1986 to parents from Afghanistan, and lived in Port St. Lucie, Florida, about a two-hour drive southeast of Orlando. The Orlando police department released a photo of him on Sunday afternoon.Amaq news agency claims Orlando attacker was affiliated with the Islamic State — Loveday Morris (@LovedayM)June 12, 2016
Hopper, the FBI agent, said Mateen was questioned twice in 2013 for comments he made at work about possible contacts with terrorists, and in 2014 for possible ties to an American suicide bomber."The FBI investigated and interviewed Mateen, and found contact was minimal and that he was not a threat at that time," Hopper said.According to Reuters, three US officials familiar with the massacre investigation said that no evidence had yet been found of a direct link with the Islamic State or any other militant group.Suspect identified as Omar Mateen, 29. An American citizen born in New York. — Orlando Police (@OrlandoPolice)June 12, 2016
Follow VICE News on Twitter: @vicenewsReuters contributed to this report.Related: America's LGBT Community Is Reeling After the Orlando Nightclub Massacre