The 81-year-old star was reportedly undergoing an operation on her throat when she stopped breathing.
According to TMZ, Joan was having the surgery at a clinic and the procedure was on her vocal cords. The site reports she stopped breathing, which is when she was taken to Mount Sinai Hospital in New York City.
The comic star's daughter Melissa is said to be on her way to be with her mother.
At the moment no further information is available and the specifics of Joan's operation have not been released.
Joan is best known for her acerbic tongue, which she regularly shows off on TV show Fashion Police! in which she and a panel comment on stars' outfits. Just this week singer Jessie J appeared on the programme, with the group discussing the looks donned at the Emmy Awards in Los Angeles on Monday.
As well as passing comment on clothing, Joan often talks about other stars. Justin Bieber has come in for a tongue lashing in the past, although recently the comedian insisted she is generally misunderstood.
"Every day there's a regret, but I don't dwell on the past," she told the US edition of OK! magazine. "I know this sounds corny, but, in real life, I try to be as nice as I can be. As I'm getting older I'm getting crankier, but I try to live up to that and that's all I can do."
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