Orlando - Police say approximately 20 people have been killed inside a Florida nightclub, and at least 42 were wounded.
Orlando Police Chief John Mina said authorities have not determined an exact number of people killed, but that "approximately 20" have died.
An FBI spokesperson said the mass shooting is being investigated as an act of terrorism. He reported that authorities are looking into whether this was an act of domestic or international terror, and if the shooter was a lone wolf.
Mina said the shooter was armed with an assault-type rifle, a handgun and some type of suspicious device. Police had said previously on Twitter that there was a "controlled explosion" at the scene of the shooting at Pulse Orlando. Mina said that noise was caused by a device intended to distract the shooter.
The police chief also said the suspect had exchanged gunshots with an officer working at the club, then went back inside and took hostages around 02:00. About three hours later, a SWAT team made the decision to go inside and rescue the hostages. The shooter died in a gunfight with those officers.
The club, Pulse Orlando, earlier posted on its own Facebook page just after 02:00: "Everyone get out of pulse and keep running."
The incident follows the fatal shooting on 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.