Early Sunday morning, approximately 50 people were killed and at least 53 were wounded at a crowded gay nightclub in Orlando, Florida, after a heavily armed gunman began shooting, took hostages, and was ultimately killed by police. The mass shooting is being investigated as a terrorist attack, either domestic or international, officials said.

A police SWAT team stormed the scene after reports of hostages emerged.

“Unfortunately there are people who died from gunshot wounds, maybe around 20, inside the night club,” Orlando police chief John Mina had said during an earlier media briefing. He said perhaps 42 injured people were taken to area hospitals, but those numbers were revised upward at 10:30 a.m. on Sunday by the city’s mayor.

The shootings began around 2 a.m. at the Pulse Orlando nightclub just as the club was about to close.

FBI Special Agent Ronald Hopper said it was unclear if the shooter acted alone, and said authorities were trying to determine if there were any connections with radical Islam, USA Today reported.

“We do have suggestions that the individual may have leanings toward that particular ideology,” Hopper said.

The suspect was identified as 29-year-old Omar Mateen. Federal law enforcement official told USA Today investigators were reviewing what the attacker may have said that would shed light on a possible terror ideology or affiliation.

The gunman was armed with an assault rifle, a handgun and some sort of unidentified device, police said.

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Also in Orlando over the weekend and prior to that incident, Christina Grimmie, a talented 22-year-old singer who rose to fame on the NBC show “The Voice,” was gunned down as she signed autographs for fans after a concert on Friday night. As she interacted with fans, a man named Kevin James Loibl, 27, of St. Petersburg, Florida, came up to her and shot her in the head, police said.

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He apparently came to Orlando specifically to carry out the attack, authorities said.

Grimmie’s brother, Marcus Grimmie, was with the singer at the time and tackled the gunman to the ground after the shots rang out — at which point Loibl then fatally shot himself, CNN and others reported. Police said Marcus Grimmie’s swift action may have saved the lives of other people.

Christina Grimmie was taken to the hospital, where she was pronounced dead.

Marcus Grimmie called his sister “a superstar. A goofball. Introverted. And a friend to everyone. Genuinely. But above all … she was my baby sister.”

Adam Levine, the Maroon 5 frontman who coached Christina Grimmie to a third place finish on season 6 of “The Voice,” mourned the singer’s death and posted on social media on Saturday, “Behati [his wife] and I are absolutely devastated and heartbroken … Christina was a natural, a gifted talent that comes along so rarely … This is yet another senseless act of extreme violence.”

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This article has been updated to reflect the latest official number of casualties and victims.