Multiple US airlines said they were beginning to resume operations Friday following a major worldwide computer systems outage that grounded or delayed thousands of flights across the country.

The IT issue has wrought global havoc at airports, grounding flights in Europe and the United States, while also derailing television broadcasts in the UK and impacting telecommunications in Australia.

At Dulles International Airport outside of Washington, Evyn Garson told AFP she and her family had been trying to travel to Florida for a wedding, but now "feel kind of stuck."

"We definitely considered just driving down there. But now it looks like they are checking bags so we might stay."

American Airlines said in a post on X that it had been able to "safely re-establish our operation" as of 5:00 am EST (0900 GMT) following a "technical issue with a vendor."

United Airlines also said on X that "some flights are resuming" as it worked to restore full operations.

And Frontier reported that it was "gradually normalizing" and "in the process of resuming flight operations," with its ground stop now lifted.

The issue was apparently caused by an update to an antivirus program, with Microsoft saying in a technical post on its website that the problems affected users of its Azure cloud platform running the cybersecurity software CrowdStrike Falcon.

The US Federal Aviation Administration (FAA), which had earlier Friday announced the grounding of US carriers over communication issues, said later it was "closely monitoring a technical issue impacting IT systems at U.S. airlines."

It said several US airlines had requested its "assistance with ground stops for their fleets until the issue is resolved."

More than 1,040 US flights were canceled and approximately 1,700 delayed as of Friday morning, according to tracking service FlightAware.