Southwest Airlines' nationwide computer woes, which started early Wednesday afternoon, turned into a full-fledged meltdown, with 600 to 700 flights canceled or delayed on Wednesday and projections of continued problems on Thursday.

As of 9:15 p.m. Phoenix time, the airline's website and computer reservations system was still down. Travelers were unable to check in online, book tickets or check flight status. The error message apologizes for the airline's "major outage.''

An employee at the airline's Phoenix telephone reservations center said employees were answering a flood of calls but unable to help passengers on any front because their computer systems were frozen. One said they were staring at a never-ending hourglass on the screen.

The only thing that appears to be working is Southwest's mobile app, though the accuracy of the information is unclear. For a 7:05 a.m. Thursday departure from Phoenix to Las Vegas, for example, the app shows an on-time departure from Gate C7.

The airline, which has one of its busiest operations at Phoenix Sky Harbor International Airport, issued this update just before 8 p.m. Arizona time Wednesday:

"Southwest Airlines is reducing the number of flights departing after 9:00 p.m. Central Daylight Time Wednesday evening in an effort to fully restore our system for tomorrow's operation. Flexible rebooking accommodation will be available to Customers once our systems are fully functional. Customers who are booked to travel tomorrow, Thursday, July 21, should check flight status information on Southwest.com and plan to arrive to the airport early, as longer than typical lines are likely. Our teams are working diligently through the night to resolve issues as quickly as possible. Southwest Airlines began experiencing intermittent performance issues earlier this afternoon with multiple technology systems as a result of an outage. Flight delays across our network have resulted in 600-700 canceled and delayed flights. Systems are gradually coming back online and we continue to move toward a normal operation. We sincerely apologize to our customers whose travel plans have been impacted.''

The statement does not address how travelers will be able to access flight status if the airline's website is still down. The 600 to 700 flights nationwide represents 17 percent of Southwest's 3,900 daily departures. Out of Phoenix late Wednesday night, the airline canceled flights to destinations including Denver and San Diego, San Francisco, Los Angeles, Sacramento and Santa Ana, Calif., according to FlightStats.com. A Southwest spokesman said 30 flights nationwide have been proactively canceled for Thursday nationwide.

At Phoenix Sky Harbor International Airport on Wednesday, a line of customers snaked in front of the Southwest check-in desk in Terminal 4 for the majority of the afternoon. Airline officials darted back and forth along the line, hectically answering questions and directing customers to waiting areas or information kiosks.

At one point in the afternoon, Southwest grounded all of its flights, which resulted in delays for some customers and cancellations for others.

Southwest has more than 170 daily non-stop flights from Sky Harbor.

Late Wednesday night, a Sky Harbor official said restaurants and retail shops in Terminal 4 were keeping extended hours.

Jill Donovan was planning on flying out of Sky Harbor with seven of her co-workers to attend an out-of-state corporate event. She was told her flight was canceled once she reached the check-in desk. She said she and her co-workers were unsure whether they would be able to join the rest of their company for the event.

Ray Mercado had to put his job on hold due to the delays. Mercado, who delivers vehicles professionally, was supposed to fly out of Phoenix to Tulsa, Oklahoma, to pick up a school bus and drive it back to Phoenix. As of Wednesday afternoon, Mercado was unsure whether he would spend his night driving a bus or sleeping on the floor of Sky Harbor.

While many of the customers were understandably annoyed by the delays, Rodney Benton was content knowing the problem posed no danger to a passenger for whom he was waiting.

"My dad is 93; he's flying in from Austin. Honestly, in this day and age, as long as he's safe, that's all I care about, so a few-hour delay isn't a big deal to me," Benton said.

Travelers going to the airline's website, Southwest.com, Wednesday afternoon were greeted with this message: "We're working hard to get you where you want to be. Please do not refresh your browser. We will automatically transfer you to Southwest.com as soon as possible. Thank you for your patience.''

The problems come during the hectic summer travel season. Last summer, Southwest also had major computer woes during its twice-a-year fare sale. Those problems lingered a couple of days.