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.
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."