The comedienne Joan Rivers is at Mount Sinai Hospital now, according to TMZ, which adds that she's currently in critical condition.

TMZ hears that she "was rushed to a hospital... after she stopped breathing during a surgery on her throat ... TMZ has learned. We're told Rivers was undergoing the throat procedure in a clinic (specifically on her vocal chords) ... when she stopped breathing during the surgery." Apparently the 911 call made at 9:39 a.m. recorded someone saying, "We have somebody in either cardiac or respiratory arrest."

Rivers, 81, had recently taped an episode of Fashion Police for E!. She's also been very active on Twitter:

Check back for updates as more information about her condition becomes available. She has a performance scheduled for tomorrow night in Red Bank, NJ.

Update: Page Six reports that Rivers is in stable condition, and Ken Baker from E! Tweeted, "Our own lovely living legend Joan Rivers is in stable condition at Mt Sinai hospital"