Witness John Schlicher told Fox News that as he picked up his first bag, "I heard the first shot. As I did, the person right next to me fell to the ground... It was very surreal."
The shooter "was holding a handgun. He was firing into the crowd. Everyone was standing there waiting for the luggage," he said.
Video showed passengers running for safety.
There was no immediate indication of a motive for the assault, in a country where gun violence is widespread due to the ready availability of firearms.
ABC News said that the gunman had traveled from Alaska to Fort Lauderdale, with a stopover in Minnesota. According to CBS he engaged in an argument on one leg of the trip.
The suspect checked a gun inside his luggage, after declaring the weapon with airport authorities, then used it to take down his victims, CNN reported, citing law enforcement sources.
He was detained without law enforcement firing any shots, Broward County Sheriff Scott Israel told reporters.
'Lone shooter'Â
Asked whether terrorism was a possible motive, authorities told reporters at a press conference it was "too early" to tell.
Santiago, was a former member of the Puerto Rico and Alaska National Guard.
US media reported that he received a general discharge from the Alaska National Guard for unsatisfactory performance.
Mayor Barbara Sharief told CNN that the gunman "was a lone shooter, and we have no evidence at this time that he was acting with anyone else."
Hours after the shooting, which occurred shortly before 1:00 pm (1800 GMT), many passengers still huddled inside the airport awaiting the all-clear.
Responding to reports that additional shots had been fired on airport property, Israel said that "no law enforcement at this time has confirmed there's been any gunshots other than what was fired at Terminal 2."
Fort Lauderdale is a major tourist hub and beach resort in the greater Miami area, and a main starting point for travel and cruises to the Caribbean.
"All services are temporarily suspended at #FLL. Please contact your air carrier about your flight information," the airport tweeted.
- Run and hide -
Cellphone video footage broadcast by local Fox television affiliate Channel 7 showed one person lying bloodied on the floor, and several others on their knees.
A passenger named as Peter Cruise said he believed that travelers on his plane were among the victims.
"I grabbed the kids and took off running down the ramp. Told the flight attendant to let us off the tarmac, we ran to hide behind some luggage carts."
US President Barack Obama, who has been briefed on the situation, told ABC News in an interview set to air Sunday that "these kinds of tragedies have happened too often during the years that I've been president."
"I don't want to comment on it other than just to say how heartbroken we are for the families who've been affected," he said.
Governor Rick Scott rushed to the airport to be briefed on the shooting, telling reporters that those responsible would be "held accountable to the full extent of the law."
Scott said that he had contacted President-elect Donald Trump, who said that he was "monitoring the terrible situation in Florida."
"Thoughts and prayers for all. Stay safe!" Trump tweeted.
-AFPÂ
