"HE'S coming. I'm gonna die.'' 

That was the chilling text message a terrified son sent his mother as he was trapped inside the Florida nightclub which was the scene of America's deadliest single shooting on the weekend.

Mina Justice was trying to contact her 30-year-old son Eddie Justice, who texted her when the gunshots erupted at the Pulse Club in Orlando and asked her to call police.

Eddie told his mother, "Mommy I love you", before saying he was hiding in the bathroom with others.

"He's coming," one text message read. "I'm gonna die".

"The next text said: 'He has us, and he's in here with us,'" Mina Justice told reporters outside the nightclub while desperately awaiting more information about her son.

"That was the last conversation."

The texts were sent at around 2.45am on Sunday, local time.

It was not long after the gunman stormed the gay nightclub, killing 50 and injuring another 53.

The gunman has been identified as 29-year-old Omar Saddiqui Mateen, a US citizen of Afghani descent from Florida.

Ms Justice told WOFL that her son told her he was being held hostage inside a women's bathroom and that she was worried he was going to die.

"I think it's all of them in the bathroom. I could hear a lot of people crying," she told the station.

Ms Justice did not know if her son was safe when spoke with reporters.