Technical difficulties are causing delays across the Southwest Airlines system, Baltimore-Washington International Thurgood Marshall Airport said in a tweet Wednesday afternoon.

"Passengers should allow for extra check-in time," the airport tweeted.

SkyTeam 11 Capt. Roy Taylor said every Southwest gate was full as of 5 p.m. and that he was seeing Southwest flights landing. By 5:30 p.m., he said some Southwest flights were taking off.

Taylor reported that the ground stop was over but that the domino effect of delays remained.

The airline released a statement to 11 News, saying, "Southwest Airlines began experiencing intermittent performance issues earlier this afternoon with multiple technology systems as a result of an outage. 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. We have a team of experts working diligently to resolve the technical issues and their efforts have systems gradually coming back online. We expect to continue our move toward a normal operation but believe it will take time."

Anxious customers tweeted to Southwest that they could not check in for flights. The airline's website wasn't working normally -- visitors couldn't buy tickets, check in for flights, or check their flight's status.

By about 5 p.m., Southwest had canceled 16 flights, more than any other U.S. carrier, and delayed about 150 others, according to tracking service FlightAware.com.