Update: E!'s Ken Baker has tweeted saying Rivers is in stable condition:

A family friend told the Daily News that the comedienne wasn't in the clear yet.

“We are scared,” the source said. “This is not looking good. No big medical decisions will be made until (daughter) Melissa arrives.”

Original story:

Joan Rivers, the sharp-tongued comedian and proud host of a bevy of television talk shows, has been hospitalized, sources told CNN.

Rivers was rushed Thursday morning to the Mount Sinai Medical Center in Manhattan after she reportedly stopped breathing during a procedure at an uptown clinic on her vocal cords. TMZ, which broke the news, said police sources described her in "critical condition." The 81-year-old's daughter, Melissa Rivers, has reportedly rushed to the scene.

The gossip site said that someone from the clinic called 911 saying "We have somebody in either cardiac or respiratory arrest." This claim has not been verified by other news sources.

Rivers' fellow comedians took to Twitter to express support: 

Rivers has had a busy week. She covered the red carpet Monday for the Emmys, and performed Wednesday night. According to her website, she has another stand-up performance on Friday, and several appearances lined up around the country, as well as abroad.

We'll have more as this story develops.

This post has been updated.