Orlando shooting: Video shows moment gunshots erupt inside Pulse nightclub

WARNING: This story contains graphic content. Discretion is advised.

Terrifying video posted on social media appears to show the moment a gunman opened fire at Pulse nightclub in Orlando, Fla., killing 49 people.

Amanda Alvear, 25, shared the footage with friends on Snapchat and it was uploaded to Facebook by user Stichs Nbc.

“Found out thru snapchat my friend Amanda Alvear was there at Pulse last night. Tried calling and texting and still haven’t gotten a reply,” the Facebook post reads.

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In the video Alvear, is seen dancing in the club with friends in a series clips, before sharp bursts of gunshots can be heard in the background. With a look of terror on her face, she says ‘shooting’ before the video ends.

On Monday, officials confirmed Amanda and her friend Mercedez Marisol Flores, 26, were killed in the worst mass shooting in U.S. history.

Her brother Brian Alvear also posted on Facebook about the death of his sister.

Authorities have identified Omar Mateen as the shooter who opened fire at a popular Orlando gay club in the early hours of Sunday morning spraying bullets at a helpless crowd. Forty-nine people were killed in the shooting and 53 were critically wounded.

Mateen, 29, who authorities said had pledged allegiance to the Islamic State (ISIS) in 911 calls just before the attack, died in a fire fight with SWAT team members.

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According to the Bureau of Alcohol, Tobacco and Firearms, the AR-15 semi-automatic assault rifle and handgun used in the attack were purchased legally by Mateen in Florida within the past week.

WATCH: There have been renewed calls to ban the AR-15 assault rifle after the Orlando nightclub shooting that claimed 49 lives and wounded dozens of others early Sunday morning. Marcelino Benito reports. 

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Officials said Monday all of the victims have been identified, and roughly half of their families have been informed. Most of the victims listed on the city’s website appear to be men in their 20s and 30s.

*With files from the Associated Press