ORLANDO, Fla. – A gunman wielding an assault-type rifle and a handgun took hostages and opened fire inside a crowded Florida nightclub, killing 50 people and wounding 53 others before dying in a gunfight with SWAT officers, police said Sunday.

Police Chief John Mina also said the shooter had some sort of "suspicious device." He said the suspect exchanged gunfire with an officer working at the club around 2 a.m., then went back inside and took hostages among more than 300 people inside.

About 5 a.m., authorities sent in a SWAT team to rescue the hostages, and the suspect then died in a gunfight with those officers. Mina said police have not determined an exact number of casualties, but that "approximately 20" people were dead inside the club.

Florida Department of Law Enforcement Special Agent in Charge Danny Banks said during a news conference that the mass shooting is being investigated as an act of terrorism. He says authorities are looking into whether this was an act of domestic or international terror, and if the shooter was a lone wolf.

"This is an incident, as I see it, that we certainly classify as domestic terror incident," Orange County Sheriff Jerry Demings said.

FBI Special Agent in Charge Ron Hopper said there's no further threat to Orlando or the surrounding area.

When asked if the gunman had a connection to radical Islamic terrorism, Hopper said, "we do have suggestions that individual has leanings towards that."

Police had said previously on Twitter that there was a "controlled explosion" at the scene of the shooting at Pulse Orlando, a popular gay dance club. Mina said that noise was caused by a device intended to distract the shooter.

Dozens of police vehicles, including a SWAT team, swarmed the area around the club. At least two police pickup trucks were seen taking what appeared to be shooting victims to the Orlando Regional Medical Center.

Pulse Orlando posted on its own Facebook page about 2 a.m.: "Everyone get out of pulse and keep running." Just before 6 a.m., the club posted an update: "As soon as we have any information we will update everyone. Please keep everyone in your prayers as we work through this tragic event. Thank you for your thoughts and love.

As soon as we have any information we will update everyone. Please keep everyone in your prayers as we work... https://t.co/3EY0fQ926m — Pulse Orlando (@pulseorlando) June 12, 2016

The incident follows the fatal shooting late Friday of 22-year-old singer Christina Grimmie, who was killed after her concert in Orlando by a 27-year-old Florida man who later killed himself. Grimmie was a YouTube sensation and former contestant on "The Voice."

Jon Alamo said he was at the back of one of the club's rooms when a man holding a weapon came into the front of the room.

"I heard 20, 40, 50 shots," Alamo said. "The music stopped."

Clubgoer Rob Rick said it happened about 2 a.m., just before closing time.

"Everybody was drinking their last sip," he said.

He estimated more than 100 people were still inside when he heard shots, got on the ground and crawled toward a DJ booth. A bouncer knocked down a partition between the club area and an area in the back where only workers are allowed. People inside were able to then escape through the back of the club.

Christopher Hansen said he was in the VIP lounge when he started hearing gunshots.

"I was thinking, are you kidding me? So I just dropped down. I just said please, please, please, I want to make it out," he said. "And when I did, I saw people shot. I saw blood. You hope and pray you don't get shot."

He continued to hear shooting even after he emerged, where police were telling people to back away from the club. He saw injured people being tended to across the street.

Mina Justice was outside the club trying to contact her 30-year-old son Eddie, who texted her when the shooting happened and asked her to call police. He told her he ran into a bathroom with other club patrons to hide. He then texted her: "He's coming."

"The next text said: 'He has us, and he's in here with us,'" she said. "That was the last conversation."

Gov. Rick Scott called the shooting an act of terror.

"We're dealing with a tragedy right now. Our prayers go out to those impacted," Scott said. "We're a resilient state."

President Barack Obama called the shooting "an act of terror and an act of hate."

Scott released the following statement before heading to Orlando to meet with officials.

"Our thoughts and prayers are with the victims, families and all those affected by this horrific tragedy. We are a strong and resilient state and we will devote every resource available to assist with the shooting in Orlando," Scott said in a statement. "Our state emergency operations center is also monitoring this tragic incident. I have been in constant communication with Orlando Mayor Buddy Dyer, Orange County Mayor Teresa Jacobs and state and local law enforcement this morning. I would like to also thank all the first responders who quickly came to assist and help those in need."

U.S. Rep. Alan Grayson, D-Florida, who represents the Orlando area, also released a statement.

"Our thoughts and our hearts go out to the victims, their families and the entire Orlando community," the statement said. "Words cannot express the horror, pain and sadness that we feel about this terrible loss. I commend the Orlando police for their heroic efforts to save the lives of those who could be saved. Local and federal law enforcement are working right now to uncover more information about the motive and other circumstances of the shooting."