(CN) - Fifty people were killed and another 53 were wounded at a gay nightclub in Orlando, Fla., early Sunday morning in what authorities are calling an act of terror and the worst mass shooting in U.S. history.
The gunman, Omar Mateen, 29, of Port St. Lucie, Fla., a sprawling town on the state's Treasure Coast, opened fire on patrons at the Pulse nightclub shortly after 2 a.m. Sunday with an AR-15 assault rifle and a handgun, and then took scores of hostages before he was killed in a shootout with police.
"It appears he was organized and well-prepared," Orlando Police Chief John Mina said during a briefing of the news media Sunday morning.
Mina said in addition to his firearms, Mateen was also carrying a "suspicious device," although he declined to elaborate.
The FBI said he referred to the Islamic State in a 911 call he placed before the slayings.
Late Sunday, the city of Orlando released the names of seven victims. They were Edward Sotomayor Jr., 34, Stanley Almodovar III, 23, Luis Omar Ocasio-Capo, 20, Juan Ramon Guerrero, 22, Eric Ivan Ortiz-Rivera, 36, and Peter Gonzalez-Cruz, 22.
Florida Gov. Rick Scott responded to word of the carnage by stating "This is clearly an act of terrorism."
"It should make every American angry," Scott added.
The governor declared a state of emergency for all of Florida and the City of Orlando, and the two area hospitals that received victims from the shooting were for a time on lockdown Sunday morning.
At the White House, Lisa Monaco, assistant to the president for homeland security and counterterrorism, said President Obama had been briefed on incident and had directed the federal government "provide any assistance necessary to pursue the investigation and support the community."
"Our thoughts and prayers are with the families and the loved ones of the victims," the White House said.
Later, the president addressed the nation, calling the shooting "an act of terror" and an "act of hate." He ordered the flag be flown at half-staff at the White House, all public buildings and grounds throughout the United States, and at military installations, embassies and consular officers across the globe until June 16 to honor the attack victims.
Attorney General Loretta Lynch is cutting short a visit to Beijing for cybersecurity meetings with Chinese officials and returning to the United States to monitor developments in the nightclub shooting investigation.
Overseas, Pope Francis expressed "horror and condemnation" at the "homicidal folly" of the shooting.
Florida Department of Law Enforcement Special Agent in Charge Danny Banks told reporters at the scene that the mass shooting is being investigated as an act of terrorism.
He said that in the early stages of what will likely be a lengthy investigation authorities are looking into whether this was an act of domestic or international terror, and if the shooter acted alone or with accomplices.
Witnesses who were inside the nightclub at the time of the shooting said the gunfire seemed to erupt out of nowhere and continued unabated for several minutes.
Pulse Orlando posted on its Facebook page around 2 a.m.: "Everyone get out of pulse and keep running."
According to eyewitnesses, more than 100 people were inside the club when the shooting began.