Terror at Orlando Nightclub, 20 Feared Dead.

Police: Approximately 20 dead inside Florida nightclub after mass shooting

Approximately 20 people are dead inside Pulse, a gay nightclub, Orlando Police Chief John Mina said Sunday morning, just hours after a shooter opened fire in the club. At least 42 people have been transported for medical treatment, he said.

Police have shot and killed the gunman, Mina told reporters.

"It's appears he was organized and well-prepared," the chief said, adding that the shooter had an assault-type weapon, a handgun and "some type of (other) device on him."

At least nine officers were involved in the shootout, Mina said. Several coroner vans were seen traveling toward the nightclub.

One officer suffered an eye injury when a bullet struck his Kevlar helmet, said Danny Banks, special agent in charge of the Florida Department of Law Enforcement's Orlando bureau. The helmet saved the officer's life, Banks said.

The shooter is not from the Orlando area, Mina said.

Orlando authorities said they consider the violence an act of domestic terror.

The FBI is involved. While investigators are exploring all angles, they "have suggestions the individual has leanings towards (Islamic terrorism), but right now we can't say definitely," said Ron Hopper, assistant special agent in charge of the FBI's Orlando bureau.

The shooting began around 2 a.m., and an officer who was working at the club responded, Mina said. The officer engaged in a shootout outside the club, after which the gunman ran into the club.

"That turned into a hostage situation," Mina said.

Authorities were getting calls from people inside the club but away from the gunman, the chief said.

More police rushed to the scene and broke down a door with an armored vehicle, helping some 30 club-goers flee to safety, Mina said. At that point police shot and killed the gunman, he said.

CNN affiliate WKMG video captured clubgoers carrying injured people from the club.

"It's just shocking," said Christopher Hansen who was inside Pulse. He heard gunshots, "just one after another after another. It could have lasted a whole song," he said.

"Everyone get out of Pulse and keep running," the nightclub posted on its Facebook page shortly after the violence began.

Orlando police warned residents to stay away from the area, and urged people not to call their offices. They declined to provide the number of casualties, saying details will be available later. Bomb sniffing dogs are on the scene.