WASHINGTON (REUTERS) - Thousands of travellers at US airports faced delays on Friday (Aug 16) because of an nationwide outage of US Customs and Border Protection's (CBP) processing systems that lasted several hours.

In a tweet at 6.37pm EDT (2237 GMT), CBP said "the affected systems are coming back online and travellers are being processed."

It said there was "no indication the disruption was malicious in nature at this time."

Earlier, CBP said officers were processing international travellers using alternative procedures, which caused "longer than usual wait times." The computer issue was not impacting departures.

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 Jan 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 business continuity and disaster recovery capabilities to minimise the impact of system failures on the travelling public. Until such deficiencies are addressed, CBP lacks a means to minimise the possibility and impact of similar system outages in the future."

CBP told the inspector general in 2017 that as "CBP moves to a cloud computing environment, improved performance and lead testing to emulate a production environment will be included in the requirements."