Shots were fired near a ticket counter at Houston's largest airport on Thursday, and at least one person was critically injured, a Houston police spokesman said.
Houston police responded to a call that there had been a "discharge of firearms" at 1:35 p.m. at the Bush Intercontinental Airport in Houston, a police source told  MyFoxHouston.com. 
KHOU.com reports that a man fatally shot himself with an AR-15 near a security checkpoint. Reports indicate that a body was found in the lobby of Terminal B of the airport.
The Houston Police Department told KHOU.com that an air marshal fired at the suspect, but missed. The man then pulled out a pistol and shot himself.
The FAA has issued a ground stop of arriving flights to Terminal B, but departing flights from Terminal B and flights in and out of the rest of the airport are unaffected. Darian Ward, a spokeswoman for the Houston Airport System, confirmed the terminal had been closed but said the airport was still operating. Passengers who were scheduled to leave from Terminal B are being rerouted to other terminals, she said.
Houston police spokesman John Cannon says one armed man has been transported to an area hospital with life-threatening injuries.
Dale Howard, of Tomball, was at the baggage handling area of the airport waiting for his sister to arrive on an incoming flight when he heard two shots fired from the floor above. A few seconds later, he said he heard three more shots.
"People were screaming. I knew exactly what it was -- gunfire," Howard said.
Police from an adjacent station rushed in, and Howard said he directed them to the floor above.
Parts of the terminal were blocked off as police investigate.
The Chron.com reported that authorities investigating the incident believe it was an isolated event and that no search was being conducted at the terminal.
The airport announced on its Twitter feed that the terminal had been closed and passengers would be redirected to other terminals.
Greg Newburn, who was in the terminal waiting for a flight to Oklahoma City, said he was sitting in a cafe area when he heard two gunshots and after a pause, several more.
"It seemed like quite a few shots. Everyone was scrambling, running left and running right, turning tables up and hiding behind tables. Nobody knew what was happening. I couldn't tell where the shots were coming from," he said.
Newburn, from Gainesville, Fla., said it took him a few seconds to realize that the shots had come from the terminal ticketing area, near the security checkpoint. Newburn said he didn't see who had fired the shots.
Officials say an autopsy will be conducted on Friday.