Rivers was getting her vocal cords checked at a clinic in New York when she started fighting for breath. She was rushed to Mount Sinai Hospital and placed in a coma as members of her family were alerted to her condition, reported New York Daily News online.
Doctors will take the 81-year-old artiste out of the coma this weekend and assess any damage.
"She's not conscious, but she's stable," Rivers' aide Graham Reed said.
Initial reports suggested Rivers was in a critical condition.
The comedienne's daughter Melissa has reportedly flown to New York from her home in California to be at her mother's bedside.