(CNN) -- Hours after a security breach forced the closure of a terminal at the Newark, New Jersey, airport Sunday, authorities were still searching for a man who went the wrong way through a checkpoint exit.
The incident happened at about 5:20 p.m. at Terminal C, when an individual walked from the public side to the secure "sterile" side for passengers who had cleared screening, according to the Transportation Security Administration.
No flights were allowed to leave from Terminal C Sunday evening and thousands of other travelers who had reached the sterile area after going through checkpoints were moved back to the public area to be re-screened, the TSA said.
Authorities are reviewing video from airport cameras. They are not sure whether the man was once on the sterile side and went back, or if he never went through screening, TSA spokeswoman Anne Davis said.
The incident caused arrival delays and mainly affected Continental Airlines, which is the airport's largest tenant.
CNN's Alina Cho, who arrived at the airport Saturday night on a flight from Fort Lauderdale, Florida, described the hectic scene: "For the people who are hoping to fly out of Newark this evening, there is not a lot of movement."
She said many passengers who had already boarded outgoing flights had to get off planes to be re-screened.
"I just saw one woman pleading with a gate agent, saying that she had two small children and a heart condition -- that she simply could not take this," Cho said. "But of course, there will be no exceptions."
Newark Liberty International Airport, which is about 15 miles from Manhattan, is the second-largest hub for Continental.
The airport handles about 35 million passengers a year.
CNN's Susan Candiotti and Ross Levitt contributed to this report.