There was chaos at one of America’s busiest airports, when authorities shut down a terminal after a man got through security without being checked.

Terminal C at Newark International near New York was closed for six hours when the man was spotted airside, sparking a major alert.

Thousands of passengers who had already cleared security were moved through the checks again and all flights in and out were stopped. Despite a widespread search the man was not found.

The alert came on the day the United States upped its security measures aimed at 14 countries.

Air travellers heading for the US from countries America believes either sponsor terrorism, or pose a security risk are having full-body checks; their hand-luggage is being searched and they could be subject to sophisticated tests for explosives.

At Frankfurt Airport precautions were stepped up after the Christmas Day attempt to attack a plane bound for America.

Chief Inspector Nicole Ramrath of Frankfurt’s Airport Police said: “The airport security measures, which were already very high, were extended after the Detroit incident. Travellers should expect to be checked more than once, and that could also mean bags being re-checked.”

But despite the more stringent measures at one of Europe’s busiest hubs, there were few complaints from passengers.

“Security doesn’t bother me,” said one. “I feel like it is for our safety so it doesn’t bother me.”

The UK Prime Minister has said his government has given the go ahead for British airports to introduce full-body scanners.

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