The gunman has been identified as Omar Mateen, 29, and he opened fire at 2am Sunday local time (Sunday evening in Australia) at the Pulse nightclub in Orlando, Florida.
Horrifying texts are now coming to light from terrified, trapped clubbers who realised what was happening.
Mina Justice told the Associated Press that she received a text at 2:06am from her 30-year-old son Eddie. “Mommy I love you. In club they shooting”.
Although Justice had been asleep she quickly texted her son back: “U ok”
He responded: “Trapp (sic) in bathroom. I’m gonna die”
It has not been confirmed whether Justice’s son, an accountant, is among the 50 casualties or additional 50 people injured.
US President Barack Obama branded the “horrific massacre” an “act of terror and hate”.
According to The New York Times, Mateen - who was killed by police when they stormed the club at 5am and freed 30 hostages - was known to the FBI.
He rang 911 prior to the attack and made comments in support of ISIS. However, the ABC says that authorities have cautioned that they have no conclusive evidence he had any direct contact with the terror organisation.
Orlando Police Chief John Mina has described the shooting as the “darkest day of my 25 years at the Orlando Police Department”.