Delta Air Lines Inc. said Monday it canceled hundreds of flights and delayed thousands of others due to a computer power outage.

The company said it canceled 650 flights following system failure at its Atlanta headquarters. The company lost power around 2:30 a.m. at its Atlanta hub but gradually resumed it six hours later.

The airline later tweeted that “systems are down everywhere.”

At 3:40 p.m. EST, Delta said it operated more than 2,300 of its nearly 6,000 scheduled flights. By that time, Delta was able to fully recover a system and resume flights but delays and cancellations continued, according to a statement from the company. Flights that took off before the outage started remained unaffected.

Los Angeles Worlds Airports tweeted on Monday morning that Delta passengers need to check their flight status before traveling to the airport, adding that delays and cancellations remain in place.

Delta’s Chief Executive Ed Bastian apologized to customers in a video posted to Twitter, saying his team is “working around the clock to restore and get these systems back as quickly as possible.”

In the meantime, Delta travelers turned to Twitter to express their frustration over delayed flights.

“My baby took his first step at MSP today. Literally turned from baby to toddler waiting for our #Delta flight,” one user wrote.

The airline said it was investigating the cause of the systems’ failure.

Trade, transportation, and manufacturing reporter Olga Grigoryants can bereached at [email protected]. Follow her on Twitter @olgagrigory.