Southwest Airline delays continued Thursday morning after flights were grounded nationwide Wednesday, leaving passengers stranded at U.S. airports, while the airline worked to fix a computer glitch.

A company spokesman tells NBC Chicago that systems were gradually coming back online, but the website remained down several hours after the issues began at about 2 p.m. CT.

In a tweet Wednesday evening, the airline said it would be offering "flexible accommodations for rebooking your travel" once its systems resumed "full functionality." [[387713142, C]]

Earlier, Southwest said in a statement that a temporary ground stop was put in place Wednesday for flights that had not left the gate as the company dealt with issues on "multiple technology systems as a result of an outage."

Southwest said in the statement: "We are now managing flight delays across our system, with a temporary ground stop in place for those flights that have not left the gate. We apologize to our Customers whose travel plans are impacted."

The website remained down as of 7:30 p.m. ET. The airline did not say what systems were down, but indicated a team was getting systems back online.

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"We are aware and investigating current issues with our systems. We will keep you posted as we have more information to share," Southwest's official Twitter account said at first, as many on Twitter expressed bewilderment at unexplained flight delays.

"Functionality continues to experience intermittent performance issues and we have some manual systems in place," a representative said Wednesday evening.

A spokeswoman for the Norm Mineta San Jose Airport said that a computer issue caused Southwest flights to be grounded until the problem is fixed.

Officials at Philadelphia International Airport said the issue was expected to persist throughout Wednesday evening. Ten flights scheduled to depart through 7:40 p.m. were not able to take off.

NBC Bay Area's John Zuchelli contributed to this report.