Snapchat killings: The moment Orlando gunman Omar Mateen opened fire inside club

WARNING: The following video below contains scenes some viewers may find upsetting

One of the Orlando massacre victims filmed the moment gunshots rang out as Omar Mateen carried out his massacre in Pulse nightclub.

Amanda Alvear, 25, shared the footage with friends on Snapchat.

During the night she had posted a series of upbeat videos that showed her friends dancing to Latin music.

But in the final clip on her profile, the night turns into a horror scene. Amanda tries to explain to the camera what is happening as quickfire gunshots blast in the background.

Clutching her face and looking fearful, she whispers 'shooting' then turns and the video cuts.

On Monday, Amanda was confirmed as one of the 49 people killed in the worst mass shooting in US history.

The brief video clip was posted on Facebook by Amanda's brother Brian.

It shows people raising their glasses and dancing to loud music before the ominous last scene.

In a status, he wrote: "People keep asking? Yes this is Amanda, she was creating a snapchat story though the night this is the last time anyone saw her, after this she did receive and answer one call."

Before her death was confirmed, Brian said that the last thing he heard about his sister was that she was hiding in a bathroom.

He said: "A lot of hostages were in the bathroom, last I heard that's where she was."

He said his sister, from Davenport, Florida, was a nursing student at the University of South Florida.

The family launched a desperate search for her and her friend, Mercedez Flores, are they were not heard from following the shooting, which was called an act of terrorism by authorities and President Barack Obama.

One of Alvear's friends was wounded in the attack and was recovering in hospital, her brother said.

Mateen killed 49 people and wounded more than 50 others after he opened fire inside and outside the gay club early Sunday morning.

According to the FBI, Mateen, 29, of Port St. Lucie in Florida, reportedly laughed as he sprayed bullets into the crowded club before he was shot dead by a SWAT team several hours after launching his horrific massacre with a legally bought assault rifle and pistol.

Although US officials do not know if the attack was directed by Isis, Mateen, who worked as a security guard, was inspired by the terror group and has been investigated by the FBI three times over his suspected terror links.

He also attended the same Mosque as an American suicide bomber.

Isis's Amaq news agency said the terror group was responsible for the shooting and says Mateen was one of its fighters.

During the attack, Mateen also referenced the 2013 Boston Marathon bombing, a Massachusetts State Police spokesman said.

Mateen, who has a wife and young son, has been described as a "mentally ill" loner who beat his ex-wife for not completing household chores and became enraged when he saw two men kissing months before launching his attack.

Gunman Omar Mateen carried out the worst mass shooting in US history.

So far, 26 victims have been officially identified by the city of Orlando on its website.

On Sunday, Edward Sotomayor Jr., 34; Stanley Almodovar III, 23; Luis Omar Ocasio-Capo, 20; Juan Ramon Guerrero, 22; Eric Ivan Ortiz-Rivera, 36; Peter O. Gonzalez-Cruz, 22; Luis S. Vielma, 22 and Kimberly Morris, 37, were confirmed dead.

In the early hours of Monday morning, Eddie Jamoldroy Justice, 30; Darryl Roman Burt II, 29, Deonka Deidra Drayton, 32; Alejandro Barrios Martinez, 21; Anthony Luis Laureanodisla, 25; Jean Carlos Mendez Perez, 35; and Franky Jimmy Dejesus Velazquez, 50, were added to the list.

Later on Monday the authorities announced more names of the 50 who died: Amanda Alvear, 25, Martin Benitez Torres, 33, Luis Daniel Wilson-Leon, 37, Mercedez Marisol Flores, 26, Xavier Emmanuel Serrano Rosado, 35, Gilberto Ramon Silva Menendez, 25, Simon Fernandez, 31, Oscar Aracena-Montero, 26, Enrique L. Rios, Jr, 25, Miguel Angel Honorato, 30 and Javier Jorge-Reyes, 40 were all killed at Pulse.

Shortly before making the 911 calls, Mateen entered the crowded nightclub at around 2am carrying an AR-15 and started spraying the helpless crowd with bullets.

Witnesses said he fired relentlessly - 20 rounds, 40, then 50 and more. In such tight quarters, the bullets could hardly miss. He shot at police. He took hostages. Around 5am, authorities sent in a SWAT team to rescue them, Police Chief John Mina said.

The shooter exchanged gunfire with 14 police officers at the club, which had more than 300 people inside.

Amanda was a nursing student at the University of South Florida.

"He had an automatic rifle, so nobody stood a chance," said Jackie Smith, who had two friends next to her get shot. "I just tried to get out of there."

When the gunfire finally stopped, 49 were dead and dozens critically wounded. Thirty-nine of the dead were killed at the club, and 11 people died at hospitals, the mayor said.

The mother of one of the victims, Mina Justice, had been sound asleep when she received the first text from her son, Eddie.

Early on Sunday morning, she was outside the club trying to contact her son, who texted her when the shooting happened and asked her to call police.

He told her he ran into a bathroom with other club patrons to hide. He then texted her: "He's coming." The next text said: "He has us, and he's in here with us," she said. "That was the last conversation."

She and a dozen family and friends remained outside at a hotel that has become a staging area for relatives awaiting news.

"His name has not come up yet and that's scary," she said. "It's just, I got this feeling. I got a bad feeling."

She said her son was normally a homebody who liked to eat and work out. He liked to make everyone laugh. He worked as an accountant and lived in a condo in downtown Orlando.

"Lives in a sky house, like the Jeffersons," she would say. "He lives rich." In the early hours of Monday morning, Eddie Justice was confirmed dead.

ORLANDO SHOOTINGS TIMELINE

2:02am - Sunday, June 12 - Suspect Omar Mateen tries to enter Pulse nightclub armed with assault rifle and and handgun and is spotted by a uniformed officer.
The two exchange fire outside the club - but Mateen manages to enter the nightclub holding 320 people while still firing.
The shooting then developed in a hostage situation.
2:09am - Pulse nightclub posts a message to their Facebook desperately telling those inside 'Everyone get out of pulse and keep running'.
5.05am - Three hours after the first shooting began, a SWAT team rushed inside to rescue hostages and confront Mateen.
Members of the SWAT team detonated a controlled explosion to confuse Mateen and then nine officers exchange gunfire with terrorist - shooting him dead.
SWAT officers manage to free 30 hostages who dashed to safety.
5:35am - Orlando police confirm that the shooter is dead.
8:00am - Officials with the FBI deem the incident to be 'domestic terrorism'.
9:40am - The shooter was officially identified as 29-year-old Omar Mateen of Port St. Lucie.
10:20am - At a press conference Mayor Buddy Dyer makes the announcement that 49 people have died and 53 injured in what is now the worst mass shooting in the history of the United States.
11.54am - US Senator Bill Nelson and California congressman Adam Schiff claimed Mateen had pledged his allegiance to ISIS