Fisher, 60, was quickly rushed to a hospital Friday afternoon by Los Angeles Fire Department paramedics. The actress was stabilised, and remains in intensive care at the UCLA Medical Centre.

“I’m shocked and saddened to hear the news about my dear friend,” Harrison Ford said in a statement. “Our thoughts are with Carrie, her family, and friends.”

Ford and Fisher worked alongside each other in the first three Star Wars films as Han Solo and Princess Later. They later reprised those roles in Episode VII: The Force Awakens in 2015.

Other Star Wars co-stars expressed their concerns for Fisher on Friday.

“As if 2016 couldn’t get any worse … sending all our love to Carrie Fisher,” said Mark Hamill, who played Luke Skywalker.

Chewbacca actor Peter Mayhew said: “Thoughts and prayers for our friend and everyone’s favourite princess right now.. Carrie Fisher.”

Star Wars star Carrie Fisher suffers heart attack on flight

“At last I know what I want for Christmas,” said Anthony Daniels, who played the android C-3PO. “The galaxy’s beloved Princess, fully functional once more. And soon.”

Fisher’s brother, Todd Fisher, told Entertainment Tonight that he was wary of making any predictions regarding her progress, given her status in the ICU.

“We certainly do not know her condition, that’s why she is in ICU. I’m sure everyone wants to speculate, but now is not the time for that,” he said. “If everyone could just pray for her, that would be good.”