“#CustomsApocalypse.”

The US Customs and Border Protection agency’s computer system experienced a nationwide shutdown Friday — causing major delays and massive lines at airports.

“This is really a big deal,” wrote one Twitter user.

“Arriving passengers to be processed manually, potentially taking hours,” another said.

Travelers at numerous airports — including Dulles, JFK, Seattle-Tacoma and San Francisco International — were experiencing delays as a result of the system going down. Many turned to Twitter and other social media accounts to voice their outrage.

“Is there any update on the system failure at customs? We’re going to miss our connection,” tweeted Barrie King at the Twitter page for Hartsfield-Jackson Atlanta International Airport.

“This is a joke,” said Frank Cesario, who posted pictures showing hordes of people waiting at JFK.

“Hello Frank, just to let you know the Customs computer system is down nationwide,” tweeted airport officials. “The agents are processing people manually. Sorry for the inconvenience.”

A similar outage occurred in 2017, causing hours-long waits and significant delays nationwide.

“Glad I have Global Entry but don’t think it’s gonna help,” tweeted Ninis Samuel, along with a pic showing travelers waiting at JFK. “#Customsapocalypse.”

CBP officials could not immediately be reached for comment Friday.