Microsoft outage causes mass airline disruptions. Here's what to know.

Air travel is experiencing disruptions across the globe on Friday morning due to a Microsoft outage for customers of its 365 apps, including many major airlines.

In the U.S., more than 3,000 flights within, into or out of the U.S. had been canceled as of 9 p.m. Eastern Time, while more than  11,400 flights had been delayed, according to FlightAware, a flight tracking service.

Airlines said the outage impacted the back-end systems they use to send key data, such as weight and balance information, required for planes to depart.

Air travelers posted images on social media of long lines at ticket counters, and "blue screens of death" — the Microsoft error page when its programs aren't working — at screens at various airports. The issue was caused by a software update sent from cybersecurity firm CrowdStrike to Microsoft, and which it said it had identified in its systems and was working to resolve.

"In a nutshell, this is PR nightmare for CrowdStrike and Microsoft and others get caught in this tornado along with millions of people currently stranded at airports around the globe," Wedbush analyst Dan Ives said in a report.

Travelers in Europe are also facing disruptions, with Lufthansa, KLM and SAS Airlines reporting issues. Switzerland's largest airport, in Zurich, said planes were not being allowed to land, according to CBS News partner network BBC News.

In Australia, airline Jetstar canceled all flights from the Brisbane airport for the day, according to the BBC. One traveler in Scotland told The Guardian she paid $8,600 for new tickets back to the U.S. after her original flight was canceled due to the IT outage.

Delta Air Lines

At about 7:50 a.m. Eastern Time, Delta said it resumed some flights after an airline-wide pause earlier on Friday morning due to the Microsoft outage. Delta had canceled more than 1,000 U.S. flights as of 9 p.m., FlightAware data shows.

"We are working to resolve the issue as quickly as possible to resume operations," Delta said in its statement.

United Airlines

United said it has been able to resume some flights, but warned customers to "expect schedule disruptions to continue throughout Friday." More than 500 United flights had been canceled as of 9 p.m. ET Friday, although some flights left from Newark airport this morning.

The airline added, "We have issued a waiver to make it easier for customers to change their travel plans via United.com or the United app."

American Airlines

American said it has restarted its operations at about 5 a.m. Eastern Time. FlightAware data shows that more than 380 American flights had been canceled as of roughly 9 p.m.

Alaska Airlines, Southwest, Frontier

Alaska Airlines told CBS News that is functioning normally. Southwest and Frontier also appear to be operating normally.

— Kris Van Cleave contributed to this report.