UPDATE: Carrie Fisher's mother, legendary actress Debbie Reynolds, posted an update on Fisher's conditon on Twitter Christmas afternoon. Reynolds says that Fisher is in stable condition, and that the family will let everyone know if there are any changes in her condition.

UPDATE 12.24.2016: Carrie Fisher remains in the intensive care unit of a Los Angeles hospital, after suffering what is being described as a serious cardiac event on a flight Friday afternoon. Her half-sister, Joely Fisher, posted a message Saturday on Twitter, thanking everyone for the love and prayers.

Read the original report below.

TMZ reported that Fisher, 60, had a massive heart attack on a United Airlines plane Friday.

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The celebrity gossip website reported that, according to unnamed sources, the actress best known for her role as Princess Leia in the original "Star Wars" franchise was on a flight from London's Heathrow Airport to Los Angeles International airport when she went into cardiac arrest.

Brad Gage, a comedian who claimed to be sitting in front of Fisher on the United Airlines flight, posted on Twitter that he saw her get taken off the plane by Emergency Medical Technicians.

According to The Hollywood Reporter, airport police officer Alicia Hernandez confirmed that police responded to an emergency on the plane, but did not identify the victim. The Los Angeles Fire Department said in a medical incident report that "LAFD firefighter paramedics were standing by for the plane's arrival, provided Advanced Life Support and aggressively treated and transported the patient to a local hospital."

The Los Angeles Times reported that Fisher is in critical condition after being rushed to the hospital and cited emergency officials who said she had a "cardiac episode."

A source not authorized to speak publicly about the incident told the LA Times Fisher was "in a lot of distress on the flight." A pilot on the flight in air traffic control audio obtained by the LA Times can be heard saying a passenger was unresponsive.

Variety reported that United Airlines issued a statement about the incident Friday:

Medical personnel met United flight 935 from London to Los Angeles upon arrival today after the crew reported that a passenger was unresponsive. Our thoughts are with our customer at this time and any requests for additional information should be directed to local authorities.

According to a 7:55 p.m. local time report, Fisher's brother, Todd Fisher, told The Associated Press his sister was being treated at an intensive care unit but he would not say what her condition was, although she was getting excellent treatment. Earlier, around 4 p.m. local time, he told The AP his sister was in stable condition and "out of emergency" and that he could not elaborate about the incident. He also said it was not clear what caused the emergency and later said there were not clear details about his sister's condition.