Her brother, Todd Fisher, told The Associated Press that she was "out of emergency" and stabilized at a Los Angeles hospital Friday afternoon. He said he could not discuss any other details about what happened.
After the plane landed at Los Angeles International Airport on Friday, the Los Angeles Fire Department responded and administered CPR prior to transporting the actress to a nearby hospital.
Eyewitness News has learned she is in critical condition on a ventilator at UCLA Medical Center.
PHOTOS: Carrie Fisher through the years
United Airlines released the following statement corroborating the incident:
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
The 60-year-old actress is best known for her role as Princess Leia on "Star Wars."
I ask everyone to stop for a moment and send special thoughts to @carrieffisher.— William Shatner (@WilliamShatner) December 23, 2016
The Associated Press contributed to this report.