In this photo provided by Twitter user Brenna but in Leo Season, travelers stand in long lines to clear customs at John F. Kennedy International Airport, Friday, Aug. 16, 2019, in New York, due to a temporary computer outage that affected U.S. Customs and Border Protection. Credit: Brenna but in Leo Season | AP

Long lines formed at international airports across the United States on Friday after U.S. Customs and Border Protection’s computer system broke down and dramatically slowed the processing of thousands of people arriving from abroad, including U.S. citizens.

Officials say they would not stop processing passengers, but said they had to switch to a slower, alternative process.

It was not immediately clear how long people were having to wait, but reports on Twitter showed clogged terminals and extremely long lines.

“U.S. Customs and Border Protection is experiencing a temporary outage with its processing systems at various air ports of entry and is taking immediate action to address the technology disruption,” the Department of Homeland Security agency said in a statement. “CBP officers continue to process international travelers using alternative procedures until systems are back online. Travelers at some ports of entry are experiencing longer than usual wait times and CBP officers are working to process travelers as quickly as possible while maintaining the highest levels of security.”

Officials said all travelers were being screened against national security-related databases and there was no sign the outage was malicious.

Reports of frustration emerged on Twitter Friday afternoon, and Los Angeles International Airport said it dispatched its team of “Guest Experience Members to help at @CBP customs areas to help direct guests and provide other assistance.”

“@CBP systems are experiencing an issue which appears to be impacting multiple airports including LAX,” the airport said. “Officers are processing passengers manually so please check with your airline for the latest status of any flight impacts. More details as they become available.”

Officials at Washington Dulles International Airport said they learned about the CBP outage at about 3:30 p.m. Friday, but they said the matter was resolved by 5 p.m.

“Processing procedures are beginning to return to normal,” said Kristin Clarkson, a spokeswoman for the Metropolitan Washington Airports Authority, the agency that runs Dulles. “Over about an hour and half period it was backed up. Those people will have to be processed. I’m not sure how long it will take.”

At about 6 p.m. Friday, John F. Kennedy International Airport in New York tweeted that passengers were “being processed manually.”

“Delays are expected,” the tweet said.

Earlier in the day, JFK airport had tweeted that “CBP staffing changes” had also led to long waits in customs, and airport officials asked passengers for “patience and understanding.”

CBP processes more than 350,000 incoming international air passengers and crew members on a typical day, according to its web site, and has experienced computer outages in the past.

CBP reported outages on its Twitter account on Jan. 1, 2018, and on Jan. 2, 2017, which led to hours-long delays each time, and a 90-minute outage on Oct. 14, 2015.

After the 2017 outage, the Homeland Security Inspector General said “underlying issues,” such as “deficient” software maintenance, “might result in future outages.”