Star Wars actress Carrie Fisher is in a "stable" condition after she suffered a medical emergency on a London to Los Angeles flight.
The 60-year-old, who starred as Princess Leia in the sci-fi franchise, was being treated in a hospital intensive care unit after the incident which prompted well-wishes from fans and stars.
Her mother Debbie Reynolds tweeted on Christmas Day: "Carrie is in stable condition.If there is a change,we will share it. For all her fans & friends. I thank you for your prayers & good wishes."
Celebrity website TMZ, which first reported the incident, said anonymous sources told them the actress suffered a heart attack.
Star Wars actor Mark Hamill, who played Luke Skywalker alongside Fisher, sent a Christmas message to his "super cool space sis" on Twitter, saying: "Wishing each & every one of you a #HoneyOfAHoliday! (especially my #SuperCoolSpaceSis @carrieffisher) #XmasPrincessPleaseComeHome."
Harrison Ford, who played Han Solo opposite the actress, said in a statement: "I'm shocked and saddened to hear the news about my dear friend. Our thoughts are with Carrie, her family and friends."
Los Angeles Fire Department spokesman Erik Scott said paramedics administered advanced life-saving care to a patient at Los Angeles International Airport (LAX) on Friday and transported the person to a nearby hospital. He did not identify the patient.
United Airlines said a passenger on flight 935 was "unresponsive".
A spokeswoman for police at LAX airport said: "Los Angeles police responded at 12.15pm to Terminal 7 regarding a female victim who went into cardiac arrest.
"Upon arrival the LAFD (Los Angeles Fire Department) was already performing CPR on the victim and the victim was transported to a local hospital for further medical treatment."
It was reported that Fisher was given CPR by passengers on board before the plane landed at LAX, where paramedics tried to resuscitate her for 15 minutes before finding a pulse.
US YouTube star and actress Anna Akana had tweeted about seeing Fisher fall ill.
She said: "Don't know how else to process this but Carrie Fisher stopped breathing on the flight home. Hope she's gonna be OK.
"So many thanks to the United flight crew who jumped into action, and the awesome doctor and nurse passengers who helped."
Actress Sally Field tweeted: "Merry Christmas or whatever you celebrate to everyone! Especially thinking of @carrieffisher with all my heart and soul."