Local officials estimate that at least 50 people have been killed after a gunman — now identified as 29-year-old Omar Mateen — opened fire early Sunday morning in Pulse, a gay nightclub in Orlando.

At least 53 people, including an officer, were injured. Police shot the gunman on the scene.

“It’s appears he was organized and well-prepared,” Orlando Police Chief John Mina told reporters at a Sunday morning press conference, pointing out that Mateen was carrying an “assault-type” weapon in addition to a handgun, CNN reports.

“This is an incident...that we certainly classify as a domestic terror incident,” Orange County Sheriff Jerry Demings added.

A chilling Facebook post from Pulse Orlando, telling guests to "run."

photo: Facebook/Pulse

The shooting comes just days after the city's "Gay Days" festivities, which culminated on June 6. According to USA Today, "it is one of the largest gay pride events in the world."

Pulse considers itself a hub for Orlando's LGBT community, calling itself "not just another gay club."

This is a developing story. Revelist will issue updates as more details unfold.

Update, 10:26 am ET: Police now say that at least 50 people are dead, and 53 injured. The initial count was 20 dead, 42 injured.

Update, 10:47am ET: The massacre is now being called the "deadliest mass shooting in U.S. history."

Update, 2:00 pm ET: Multiple sources confirm gunman pledged allegiance to the Islamic state before he opened fire in the nightclub  

Update, 2:08 pm ET: President Obama has spoken out, extending his sympathy to the LGBTQ community, and adding, "this was an act of terror."