ORLANDO, Fla. - A shooting and hostage situation early Sunday at a Florida nightclub -- which describes itself as "Orlando's hottest gay bar" -- left an estimated 50 people dead, including the gunman, and more than 50 injured, officials say.

Orlando Mayor Buddy Dyer said at a press conference Sunday that a state of emergency has been declared after what authorities have indicated may have been a "lone wolf" style terror attack. The attack appears to be the deadliest mass shooting in American history.

Sources have confirmed to CBS News that authorities are investigating whether the suspect, who has been named as Omar Mateen, had ties to Islamic terrorism. Mateen, of Port. St. Lucie, Florida, is a U.S. citizen with no apparent criminal history, according to sources.

Dyer said that in addition to the 50 people who were killed in the attack, 53 were treated for injuries.

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Orlando Police Chief John Mina said the suspect was found with a handgun and an AR-15-style assault rifle.

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A U.S. intelligence source told CBS news senior investigative producer Pat Milton that Islamic terrorism is being investigated as a possible motive in the shooting due to several indicators including the style of the attack, which had similarities to the attacks in Paris in November 2015 and Brussels in March. The gunman put up a protracted gun battle with police and was heavily armed, the source said.

Robots are now analyzing a device the gunman had strapped to his body to determine if it was a real explosive device or a fake made to look like a real device, the source said.

Sources tell Milton that authorities investigating the incident are still looking into whether the attack is a hate crime.

Mina said the incident at Pulse nightclub began around 2:20 a.m., when shots rang out and an officer already posted at the event engaged the gunman, whom Mina said was armed with an assault rifle, a handgun, and a "device" of some kind that officials believed was a threat. Mina said the gunman appeared organized and well-prepared for the incident.

Pulse Orlando posted on its own Facebook page around 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."

After the officer already there engaged the gunman, other law enforcement agencies and officials responded, and the gunman retreated into the nightclub and began a "hostage situation," Mina said.

SWAT officer eventually made the decision to attempt to rescue the hostages, and entered the club, where nine officers were involved in the fatal shooting of the gunman, Mina said. One officer was injured, and Mina said he believes the officer's life was probably saved by his Kevlar helmet.

Pulse shooting: In hail of gunfire in which suspect was killed, OPD officer was hit. Kevlar helmet saved his life. pic.twitter.com/MAb0jGi7r4 — Orlando Police (@OrlandoPolice) June 12, 2016

How and when the numerous deaths occurred is still being investigated, officials said.

Stuart Milk, the president of the Harvey Milk Foundation, an LGBT advocacy group, decried the "act of horrendous violence" in a statement posted to Facebook.

Mina and other law enforcement officials insisted there is no ongoing threat to the community.

As the news of the mass shooting broke Sunday morning, presidential candidates and other politicians took to Twitter to express their support for the victims.

Law enforcement sources tell CBS News the FBI is now responding, but that the Orlando Police Department is leading the investigation into the active shooting.

The incident is the second deadly shooting at an Orlando nightclub in the last week. Last Friday, 22-year-old singer Christina Grimmie was shot and 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." Mina said officials do not believe the two incidents are linked.