50 people are dead and at least 53 injured in what is being described as the worst mass shooting in American history.

Orlando Mayor Buddy Dyer on Sunday told reporters that the death toll from a terror attack on the Pulse nightclub had risen to 50 people, up from earlier reports of 20. Pulse bills itself as “Orlando's premiere gay night club.”

Police identified the gunman as Omar Mateen, a 29-year-old man from Port St. Lucie, Florida, which is located about 120 miles south of Orlando.

Police Chief John Mina said that the incident started at 2:02 AM, when Mateen and three police officers engaged in a gun battle outside the club. A SWAT team was called in as Mateen turned the incident into a hostage situation. At about 5 AM, police stormed the club, killing Mateen.

Mateen was heavily armed, carrying an assault rifle, a handgun and an unidentified “device.”

Dyer called the incident a “horrific crime … that will have a lasting effect on our community.”

FBI Special Agent Ronald Hopper said that the suspect might have “leanings” toward radical Islam and that the incident was being investigated as a possible act of terrorism, either domestic or international.

Mateen's father, Mir Seddique, told NBC News, “this has nothing to do with religion.” He added that his son got angry when he saw two men kissing in Miami a few months ago.