Eleven passengers walked through a security checkpoint without being screened before apparently boarding planes at John F. Kennedy International Airport in New York on Monday, national media reported.
The breaches occurred at about 6 a.m. local time at a checkpoint lane that was not fully staffed, NBC News reported.
The passengers' carry-on bags were screened and cleared by a security team with sniffer dogs, Transportation Safety Administration (TSA) sources told the broadcaster.
Three of the passengers set off metal detectors but were permitted to continue to their boarding gates without being body searched by staff, the broadcaster said.
U.S. authorities beefed up security at airports in 2001 following the 9/11 attacks.
A debate over whether it should be tightened further has been given impetus by a deadly shooting in January in a Florida airport baggage claim area, and attempts by President Donald Trump to clamp down on immigration from some Muslim-majority countries.
The Port Authority said three passengers were screened after they got off their flight when it landed in California.
It did not say if they were the people who had also set off the metal detectors, and gave no information about the identities or flight schedules of the other eight passengers.
The TSA said it was confident the incident presented "minimal risk to the aviation transportation system," NBC News reported.
TSA and port authority officials were not immediately available for further comment.
(Reporting by Brendan O'Brien; editing by John Stonestreet)