ATLANTA –– A man eluded guards after running through a security checkpoint at the nation's busiest airport Friday, forcing as many as 10,000 passengers to evacuate and causing a ripple effect that slowed air traffic throughout the United States.

The 11:45 a.m. security breach all but shut down Hartsfield Atlanta International Airport for four hours, as flights into and out of Atlanta were delayed on the busy travel weekend before Thanksgiving.

Police said the suspect was not captured and may have escaped in the crowds of passengers who were forced into parking lots outside the terminal.

Lines of people in the lot began moving slowly after 3 p.m. and the flights began takeoffs after 4 p.m.

The suspect, a white male wearing jogging shorts and a T-shirt, ran past guards at a security checkpoint then down an up-escalator, said Benjamin DeCosta, the airport's general manager. The man did not carry a visible weapon.

Private security workers and National Guard troops chased the man to no avail.

The Federal Aviation Administration halted departures at Hartsfield and planes in other cities destined for Atlanta were told to remain on the ground, FAA spokesman Christopher White said. International flights were allowed to land and passengers were held in the concourse.

DeCosta said from 5,000 to 10,000 passengers and employees were evacuated. Many were standing outside in the two twin parking lots around the terminal, while others were inside the main baggage area.

"If you want me to fly, you've got to stop this kind of nonsense," said Jerry Presley of Kansas City, who had been in Atlanta on business. "They should have stopped this guy. There should have been someone to catch this guy."

AirTran Airways canceled 22 flights and had to deplane 18 others that were preparing to leave Atlanta, spokesman Tad Hutcheson said. It also diverted 17 flights to airports in the region, such as Macon and Chattanooga, Tenn.

Delta Air Lines spokeswoman Peggy Estes said the number of flights delayed and canceled by the breach was not immediately available.

Commuter trains and buses were not allowed to enter the airport, stranding thousands more people.

"We'll wait it out," said Mike McDonough of Tucker, who was headed to Italy with his wife. "Hopefully, we'll get out today."

Georgia Sen. Max Cleland was among those stranded at the airport — he was supposed to take a flight to Savannah for a 4 p.m. news conference on aviation security.