Five people have died after a gunman opened fire in the baggage claim area at Florida's Fort Lauderdale airport.
The attack sent panicked passengers running out of the terminal and on to the tarmac.
Authorities gave no details on a possible motive for the shooting, which left eight other people wounded.
"People started kind of screaming and trying to get out of any door they could or hide under the chairs," a witness, Mark Lea, told MSNBC. "He just kind of continued coming in, just randomly shooting at people, no rhyme or reason to it."
Then the attacker threw down his weapon and lay spread-eagle on the ground until he was taken into custody, Mr Lea said.
Chip LaMarca, a Broward County commissioner, was briefed on the airport shooting by Broward Sheriff's office. He said that the shooter had arrived in Fort Lauderdale aboard a Canadian flight with a gun in a checked bag.
"After he claimed his bag, he went into the bathroom and loaded the gun and started shooting. We don't know why," Mr LaMarca said.
Senator Bill Nelson of Florida claimed the gunman was carrying military ID in the name of Esteban Santiago, but that it was unclear whether it was his.
"We don't know a motive at this point," Mr Nelson said. "This could well be someone who is mentally deranged, or in fact it could be someone who had a much more sinister motive that we have to worry about every day, and that is terrorism. We can't conclude that."
President Barack Obama was briefed by his Homeland Security adviser, the White House said.
President-elect Donald Trump said he was monitoring the situation and that he had spoken with Mr Scott.
Mr Trump tweeted, "Monitoring the terrible situation in Florida. Just spoke to Governor Scott. Thoughts and prayers for all. Stay safe!"
The attack took place at terminal 2, which serves domestic routes for Delta Air Lines and Air Canada's international flights.
Mr Lea said the gunman said nothing as he "went up and down the carousels of the baggage claim, shooting through luggage to get at people that were hiding". He had a handgun and went through about three magazines of ammunition, Mr Lea said.
Sheriff Scott Israel said five people were killed and eight were wounded. Their condition was not disclosed. He said the gunman was arrested unharmed, with no law enforcement officers firing any shots, and was being questioned by the FBI.
The airport suspended operations as law enforcement authorities rushed to the scene and emergency medical workers treated at least one bleeding victim on the tarmac.
People spilled on to the tarmac, some carrying luggage, and some ran from both terminals 1 and 2, hiding behind cars or anything else they could find to shield themselves.
Video posted on Instagram appeared to show several people wounded in the baggage claim area of the terminal. One person appeared to be lying in a pool of blood with a head wound.
Paramedics could also be seen treating a bleeding victim outside the airport. Hundreds of people stood on the tarmac as an ambulance drove by.
Flights already in the air and headed for the airport were delayed or diverted, and those that had yet to take off for Fort Lauderdale were held on the ground.
John Schilcher told Fox News said he came up to the baggage claim and heard the first gunshot as he picked up his bag off a carousel.
"The person next to me fell to the ground and then I started hearing other pops. And as this happened, other people started falling and you could hear it and smell it, and people on either side of me were going down and I just dropped to the ground," said Mr Schilcher, who was there with his wife and mother-in-law.
"The firing just went on and on," he said.
He said the gunman emptied his weapon and reloaded, and "it was eerily quiet".
"I was down on the floor, when we finally looked up there was a policeman standing over me," Mr Schilcher said. "That's when I assumed it was safe."