American actress Carrie Fisher on the set of "Star Wars: Episode IV - A New Hope."

Fisher, world-famous for playing Princess Leia in the blockbuster franchise, was rushed to a local hospital after suffering full cardiac arrest on a flight from London to Los Angeles. Her condition, sources said, was "not good."

The Los Angeles Fire Department was contacted about just after noon right before United flight 935 landed, and she was taken to Ronald Reagan UCLA Medical Center, where she was in critical condition, sources said.

More from NBC News:

No bond for suspect in 'road rage' shooting that killed 3-year-old

Suspected Berlin attackers shot dead after chance encounter with Italian cops

U.S. abstains as United Nations condemns Israel settlements

Two actors tweeted that they were on board the plane when Fisher fell ill.

@AnnaAkana: Don't know how else to process this but Carrie Fisher stopped breathing on the flight home. Hope she's gonna be OK



@bradgage: I'm in complete shock. @AnnaAkana and I sat in front of Carrie Fisher on our flight from London and she was just taken off the plane by EMTs

Fisher, 60, had recently wrapped filming for "Star Wars: Episode VIII," the second of three new films in the massively popular sci-fi saga.

She was promoting her eighth book, a collection titled "The Princess Diarist," in which she revealed her affair with co-star Harrison Ford.