A gunman opened fire inside a crowded gay nightclub in Orlando, killing 50 people and injuring dozens more in a rampage that turned into a deadly hostage situation, reports Washington Post.

Authorities in Orlando said that 50 people were killed in what authorities are calling an act of domestic terrorism, and many others were injured in the violence at Pulse, a popular gay bar and dance club. Police had initially thought about 20 people were killed in the attack, but authorities said later on Sunday morning that the toll was significantly higher.

Officials said the shooter was shot and killed by police officers in a shootout. It was not immediately clear if the 50 people killed included the gunman.

The suspected gunman was identified by relatives and law enforcement officials as Omar Mateen, a 29-year-old from Fort Pierce, Fla. One relative said that Mateen’s family was in shock after being told on Sunday morning about his involvement. This relative said Mateen’s family was very sorry about what had happened.

Police have not identified a possible motive, and details about Mateen’s background were scarce on Sunday morning. His family is from Afghanistan, while Mateen is believed to have been born in the United States.

“It appears he was organized and well-prepared,” Orlando Police Chief John Mina said at a Sunday-morning news conference, noting that the shooter had an “assault-type” weapon and a handgun.

At least 42 people were transported to various hospitals, Mina said, adding that one officer was wounded.

“This is an incident … that we certainly classify as a domestic terror incident,” Orange County Sheriff Jerry Demings said at the news conference. The FBI is involved in the investigation, authorities said.

“We had a crime that will have a lasting effect on our community,” Orlando Mayor Buddy Dyer said. “We need to stand strong, we need to be supportive of the victims and their families.”

Officials said Sunday they found “an assault-type rifle and a handgun” at the scene. In addition, a law enforcement official said Mateen was previously known to authorities, but said he was not under investigation.

The White House said President Obama was briefed on the incident Sunday.