US airline giant Delta says all its departing flights have been suspended due to a nationwide system outage.
“Customers should check the status of their flight before heading to the airport while the issue is being addressed,” the company tweeted.
It said it was working to resolve the problem as soon as possible. Inbound flights en route are not affected.
Delta ranks third in terms of most passengers carried, according to industry body the IATA.
What caused the outage or how long it will take to resolve has not been released.
One passenger told the BBC he was waiting with “several hundred” fellow stranded passengers at San Francisco airport, after being asked to leave a plane he had already boarded.
“We were ordered off the lane after approximately an hour or more,” said Dick Ginkowski.
“Tempers are starting to get just a little bit strained at this point,” he added. “They aren’t able to rebook anyone on other carriers.”
Delta has been responding to unhappy customers on Twitter.
Delta serves nearly 180 million customers a year, employing over 80,000 people, according to its website.
It has its headquarters in Atlanta, Georgia and began in the 1920s as a crop-dusting company.