Thousands of travellers in the US were forced to wait hours in line after a customs computer system crashed at airports around the country.
Videos posted to social media showed stagnant lines of international passengers queueing to get their passports checked.
US media reported outages at major cities, including Miami, Fort Lauderdale, Atlanta and Virginia.
“Thousands sitting in nonstop lines, no [air conditioning],” traveller Jack Brewer wrote on Twitter, adding he and his companion were “just trying return from our relaxing New Years in Haiti”.
Photos also showed luggage piling up around baggage claim carousels, with travellers unable to pick them up.
“There are thousands and thousands of people behind me,” Sara Curran wrote in Miami.
United States Customs and Border Protection (CBP) issued a statement on Monday saying a processing system outage caused delays at various airports.
CBP officers continued processing international travellers using “alternative procedures” until the system came back online.
Officers still had access to national security databases and all travellers were screened according to security standards during the outage, the CBP said.
The statement did not give a cause for the disruption but said it did appear to be malicious.
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