Passengers fill the terminal after a security breach shut down Terminal C at Newark Liberty International Airport. Photo: AP
One of America's busiest airports is in lockdown after a security scare.
Security officials shut down Newark Airport in New Jersey after a man breached security by walking on the wrong side of a security checkpoint.
Security officials have not allowed anyone to enter or leave Terminal C of the airport and dozens of planes, mostly operated by Continental Airlines, have been grounded.
Thousands of passengers are having to be re-screened by security, after the unidentified man was thought to have entered the "sterile" section of the terminal without being screened.
"A man was observed entering the sterile area of the airport from the exit lane, and we immediately froze operations," Transportation Security Administration (TSA) spokeswoman Sari Koshetz said.
Passengers who had already boarded their planes were also forced to disembark and undergo screening a second time.
"To be cautious, we wanted to make sure that everybody who gets on a plane tonight has been screened," Koshetz said.
The man who breached security was never located, a TSA spokeswoman told CNN, but all passengers were being re-screened.
Officials from the US Transportation Security Administration are unsure which way the man bypassed security, whether he went out from the secure area to the public area or in from the public concourse to the secure zone.
Security officials are scrolling through footage from the airport's closed circuit cameras in an effort to find the man.
A well-placed aviation source told Traveller that where a sterile zone was thought to have been breached, and the person had not been found, it was standard procedure to clear the sterile area and put all passengers through security screening again.
The incident comes on the first day of heightened security measures for US airports in response to the failed attempted bombing of a US-bound flight on Christmas Day.
Reports of an incident emerged at 11am Melbourne time as passengers posted messages on social networking site Twitter.
Some passengers posted messages that they saw security guards rush past, before sealing off the terminal.
US news organisation CNN reported that the airport was in shutdown after "after a man walked through the wrong side of a checkpoint exit".
Flight departures were put on hold while passengers were re-screened.
Newark International Airport is about 20 kilometres south-west of New York and handles about 30 million passengers a year.
with AFP