Thousands of travellers at US airports faced delays late on Friday (local time) because of a nationwide outage of inbound processing systems.
Customs and Border Protection (CBP) said in a statement the outage was temporary and "officers continue to process international travellers using alternative procedures until systems are back online. Travellers at some ports of entry are experiencing longer than usual wait times."
The computer issue is not impacting departures.
JFK Airport in New York said on Twitter that "the Customs computer system is down nationwide. The agents are processing people manually."
People at various US airports posted videos on social media sites of lengthy lines at processing checkpoints and several airports warned of extensive delays.
On an average day, CBP processes around 358,000 air passengers and crew.
The Federal Aviation Administration (FAA) said the outage had not caused any changes in flights.
This is not the first time the system has faced problems. The system was down for four hours on January 2, 2017 as many travellers were returning from holiday trips.
A Homeland Security inspector general's office report issued in November 2017 found "inadequate CBP software capacity testing, leaving the potential for recurrence of processing errors."
The report also warned of "inadequate… capabilities to minimise the impact of system failures on the travelling public."
CBP told the inspector general in 2017 that performance would improve as it moved to a cloud computing environment.