Washington: A lone gunman armed with an assault rifle shot and killed 50 people and injured 53 others at a gay nightclub in Orlando, Florida yesterday, in the deadliest mass shooting in the US. 50 people were killed inside the Pulse nightclub and at least 53 people were injured, police say.

Killer: Omar Mateen Killer: Omar Mateen

"It appears he was organised and well prepared," Orlando Police Chief John Mina said. The shooter had an assault-type weapon, a handgun and "some type of (other) device on him." Orlando authorities said they consider the violence an act of domes tic terror and the FBI is involved in the probe.

Police officers direct family members away from the shooting
Police officers direct family members away from the shooting

The gunman had allegedly called 911 moments before the incident to pledge allegiance to ISIS, a law enforcement source told NBC news.

The shooting started a little after 2 am. The alleged shooter, identified as Omar Siddique Mateen was killed. The deadly incident went on over a three-hour period. "The suspect at some point went back inside the club where more shots were fired. This did turn into a hostage situation," Mina said.

Christine Leinonen waits for her son, who was trapped inside. Pics/AFP
Christine Leinonen waits for her son, who was trapped inside. Pics/AFP

Shooter’s father says
Meanwhile, Omar’s father said he believed his son was motivated by hatred of gays – not by his Muslim religion. "This had nothing to do with religion," Mir Siddique told NBC News.

He said his son recently lashed out in his presence after witnessing a gay couple embracing, and suggested the incident may have triggered the atrocity. Omar was married and had a 3-year-old son.

US mass shootings over last 12 months

June 18: Dylann Storm Roof, a white supremacist opens fire at a historic black church in Charleston, South Carolina, killing nine.

October 1: Christopher Sean Harper-Merchant, (26) a student at a college in Oregon killed 8 fellow students and a teacher.

November 29: Gunman enters Planned Parenthood clinic in Colorado Springs, Colorado, kills 3, injures 9.

December 2: Married couple opens fire at holiday party in San Bernandino, California, killing 14, injuring 20.

27 The number of mass shootings in Florida in 2015, according to Shooting Tracker.

372 The number of mass shootings in the US last year, according to Mass Shooting Tracker. 475 people have died in such shootings.