*Warning: This article contains details and video that some may find disturbing.*

A video that appears to have been taken during the deadly shooting at Pulse gay nightclub in Orlando, Fla., gives a glimpse of the chilling moment gunshots started to ring out early Sunday.

The video, which was posted to Snapchat, was posted on 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.

In the video, a woman using the Snapchat account name "Amanda," is seen dancing and partying with friends inside a darkly lit club in several different short video clips. Suddenly, the sound of rapid gunfire is heard in the background as the woman, who wears dark-rimmed eyeglasses, stares into the screen with a look of horror. The video ends as the woman begins to run.

Alvear was confirmed dead on Monday, her brother said on Facebook. She was 25, according to the City of Orlando's list of the victims.

Alvear's brother also confirmed that it was his sister in the video. "Yes, this is Amanda, she was creating a Snapchat story through the night," he wrote in a separate Facebook post. "This is the last time anyone saw her, after this she did receive and answer one call."

Police say 49 people were killed after gunman Omar Mateen entered the nightclub early Sunday morning and started to open fire on the patrons. Mateen was later shot and killed by police.