A terminal at an airport serving New York has been closed off after a traveller triggered a security scare.
The alert at New Jersey's Newark International was triggered after a man apparently passed into a secure area without being screened.
The Transportation Security Administration has toughened security measures for all passengers on United States-bound flights after a failed attack on a Northwest Airlines plane flying into Detroit on Christmas Day.
Newark airport officials viewed security tapes to see if they could identify the man who triggered the scare but all passengers waiting to board flights were being re-screened.
The United States has issued new security directives for airline passengers travelling to the country after a failed bomb attack on an American plane on Christmas Day.
The tightened measures come after the US and Britain closed their embassies in Yemen for a second day amid concerns they could be targeted by terrorists.
From 4 January, there will be enhanced screening of certain passengers flying to the US, particularly from countries known to have links with terrorism, the BBC reports.
People flying from Nigeria, Pakistan, Syria, Iran, Sudan, Yemen and Cuba will have pat-down body searches and have carry-on baggage searched.
Passengers travelling from any other foreign country will also be checked at random.
The guidelines include long-term measures developed in consultation with all international carriers which fly to America and are a response the failed attempt to explode a device on a US-bound plane on 25 December.
Nigerian Umar Farouk Abdulmutallab, 23, is being held in a US prison and is accused of attempting to detonate an explosive device hidden in his underpants on a flight from Amsterdam to Detroit.
US President Barack Obama says an al Qaeda-linked organisation in Yemen appeared to have trained Mr Abdulmutallab.
Mr Obama's top counter-terrorism adviser, John Brennan, said lapses and human errors are to blame for American security services not identifying the bombing attempt and there is no single piece of intelligence that showed the suspect was a terrorist who was going to get on a plane.
Body scanners at Heathrow soon
British airport operator BAA says it will move quickly to install full-body scanners at London's Heathrow Airport after the Christmas Day incident.
The scanners will be introduced within weeks at Heathrow, Europe's busiest airport, and will be used for flights to all destinations.
Scanners will also be introduced at other airports throughout the United Kingdom.
British Prime Minister Gordon Brown defended the decision to introduce technology which enables security staff to see through passengers' clothes, saying it is among a number of measures being introduced to make air travel safer.
Mr Brown says terrorists are using new forms of weapons and the government has to respond accordingly.
There are no immediate plans to introduce similar technology in New Zealand, but aviation security officials are waiting for word from the US on the future of security measures for US-bound flights.
Aviation Security Service general manager Mark Everitt told Radio New Zealand on Monday that he expects to hear from American officials in the next day.
Mr Everitt says there have been few complaints about the extra security measures.
The BBC reports there are mounting fears that Yemen is becoming a leading al Qaeda haven, prompting the US and Britain to shut their embassies after threats from an al Qaeda offshoot linked to the Christmas Day incident.
The US has indications that al Qaeda is planning an attack in the Yemeni capital Sana'a, Mr Brennan has said.
The US mission in Yemen was the target of an attack in September 2008, in which 19 people died.
Meanwhile, Britain says it and the US will jointly fund a new counter-terrorism police unit in Yemen as part of plans to combat the threat from Islamic militants.