OKLAHOMA CITY - Several Delta Airlines flights are delayed at Will Rogers International Airport in Oklahoma City, due to the airlines’ nationwide computer outage Monday. Just before 8 a.m., however, Delta is lifting the ground stop on some flights across the country.

Monday morning, several flights are delayed at Will Rogers, including Delta 1147 that was set to arrive in Oklahoma City at 9:10 a.m. from Atlanta, Delta 1540 set to leave Oklahoma City for Atlanta at 5:30 a.m., Delta 3624 set to leave Oklahoma City for Detroit at 5:34 a.m., and Delta 4594 set to leave Oklahoma City for Salt Lake City at 6:11 a.m.

Delta Air Lines is warning passengers of "large-scale" flight cancellations Monday due to computer system issues stemming from a power outage in Atlanta, where the carrier is headquartered. Many flights were already being delayed.

Earlier, Delta tweeted that its computer systems were down "everywhere" and some flights had been "grounded," though flights already in the air weren't affected.

At 6:55 a.m. local time, Delta said in a statement, "A power outage in Atlanta, which began at approximately 2:30 a.m. ET, has impacted Delta computer systems and operations worldwide, resulting in flight delays. Large-scale cancellations are expected today. All flights enroute are operating normally.

"We are aware that flight status systems, including airport screens, are incorrectly showing flights on time. We apologize to customers who are affected by this issue, and our teams are working to resolve the problem as quickly as possible."

There were indications of progress in getting systems back up to speed. A CBS News staffer at London's Heathrow Airport reports passengers were told Delta systems were back online and passengers were being checked in.

But an airline spokesperson in the U.S. told CBS News it was still in a "ground hold" and would not confirm or deny that the systems were back up.

WGCL-TV, the CBS affiliate in Atlanta, where Delta is based, reports the problem was first uncovered when a flight was to take off from San Francisco.

Delta said flights in the air were OK:

The Associated Press reports, "Several applications were affected, including the company's website."