For a second day, Delta Air Lines canceled hundreds of flights, including dozens at Minneapolis-St. Paul International Airport, and delayed thousands more as it tried to get back to normal from a power outage at its operations center on Monday.

By late afternoon Tuesday, the airline had canceled 680 of its approximately 6,000 daily flights. MSP is the airline's second-biggest hub after its Atlanta home base.

The cancellations and delays grew throughout the day as the airline moved planes and crews back into normal positions while attempting to get as many passengers as it could where they needed to go.

By late afternoon, the flight boards at MSP showed more Delta flights were in canceled or delayed status than there had been on Tuesday morning, a reflection in part of a stackup effect as problems ripple through airline networks. Delta's longest flight from MSP, a daily flight to Tokyo, left about 3½ hours late Tuesday ­afternoon.

The company's chief executive, Ed Bastian, for a second day created a video message on Delta's website to describe the problem and to apologize. Delta's 800 canceled flights on Monday, he noted, were more than three times the number the airline had canceled in the entire year up to then.

"This isn't who we are," ­Bastian said on the video. "This isn't the quality of service, the reliability, you have come to expect from Delta."

He added that it was likely Delta would have to cancel and delay flights on Wednesday, though not as many as on Monday and Tuesday. Delta extended fee waivers and other offers that it made to passengers on Monday and provided ­thousands of hotel vouchers at its major hubs.

Monday night, Delta paid for hotels for more than 2,000 passengers in Atlanta. That night, it also asked Minneapolis-St. Paul administrators to provide sleeping mats for as many as 450 people, though the airport did not have an official tally of how many were used. Two airport restaurants stayed open all night and several others extended their hours to accommodate stranded passengers, airport spokeswoman Melissa Scovronski said.

The power outage, which happened early Monday at its Atlanta operations center, forced Delta to halt all departures worldwide for about six hours. That created a cascade of effects similar to what airlines experienced from winter snowstorms before adopting a practice several years ago of canceling flights ahead of bad weather.

"In the past, after a storm they had to reposition everything," said Seth Kaplan, an editor at Airline Weekly and author of a book on Delta. "Now when there is a blizzard coming, they will conservatively precancel thousands of flights and leave everything in a good position to quickly restart afterward."

In another post on the company's website, Gil West, Delta's operations chief, explained that crews tend to work in three- or four-day rotations that became invalid as the system shut down ­Monday. "Multiplied across tens of thousands of pilots and flight attendants and thousands of scheduled flights, rebuilding rotations is a time-consuming process," West said.

After a survey in 2010 showed Delta that passengers disliked flight cancellations more than delays, executives reoriented the airline's operations to avoid cancellations. Delta keeps more spare planes and crews at its big hubs, including MSP, and uses software to predict when airplane parts might fail, sending planes into the hangar for repairs before they do. It sometimes resorts to extraordinary steps, such as having an international flight make an interim stop to pick up a crew, to keep from canceling a flight.

Many steps Delta took to reduce cancellations led to better on-time reliability for its system overall, something the airline used to justify premium pricing that lifted revenue and profits to record levels in recent years.

"Delta has set a high standard for itself," Kaplan said. "It has billions in revenue premiums over competitors because of how reliable it is."