Customs and Border Protection computers went down nationwide Friday afternoon, delaying international arrivals at Dulles International Airport, according to the Metropolitan Washington Airports Authority.
CBP officers processed passengers manually.
Some passengers said they waited for two hours at passport control.
The computers were restored before 5:30 p.m.
"CBP is experiencing a temporary outage with its processing systems at various air ports of entry & is taking immediate action to address the technology disruption," the agency tweeted. "CBP officers continue to process international travelers using alternative procedures until systems are back online."
When the international arrivals area became too crowded, some travelers waited in the airport's mobile lounges. Others waited in planes on the tarmac.
CBP kept the dayside on to help process the delayed passengers.
It wasn’t immediately clear what caused the problem at CBP, but the agency said it will continue investigating. There was no indication that the system was intentionally derailed, according to a CPB official.