US actress Carrie Fisher, who played Princess Leia in the Star Wars films, is in a critical condition after suffering a heart attack during a flight, reports say.
She went into cardiac arrest on the London to LA flight, the LA Times said.
Passengers attempted to revive her with CPR and she was rushed to hospital when the plane landed after midday local time (20:00 GMT), the TMZ website said.
Fisher, 60, had been on tour promoting her latest book The Princess Diarist.
The heart attack happened about 15 minutes before the plane landed in LA, celebrity news website TMZ reported. A medic who was travelling on the plane administered CPR.
A law enforcement official told NBC that her condition was “not good”.
United Airlines issued a statement saying that Flight 935 from London to Los Angeles was met on the ground by medical personnel after the crew reported that a passenger was “unresponsive”, but did not name the passenger, Reuters reported.
Passengers on the plane have been tweeting about what they saw.
Fellow Star Wars actor Peter Mayhew, who played Chewbacca in the films, tweeted his thoughts and prayers for “everyone’s favourite princess”.
Fisher appeared in the original Star Wars trilogy and Star Wars: The Force Awakens, a sequel released last year.
She also appeared in other films including The Blues Brothers and When Harry Met Sally.
She has written four novels and three memoirs and was previously married to the musician Paul Simon.
In her latest memoir she reveals that she and Harrison Ford, who played Han Solo, had an affair during the filming of Star Wars when she was 19 years old, and he was 33 and married with two children.
Fisher is the daughter of singer Eddie Fisher and actress Debbie Reynolds.