Joan Rivers has been hospitalised after she was rushed from a doctor's office when she went into cardiac arrest, police and hospital officials said.
In a statement, Melissa Rivers said her mother was "resting comfortably" with family. She did not elaborate on the 81-year-old comedian's condition.
"We ask that you continue to keep her in your thoughts and prayers," Melissa Rivers said. She offered thanks for the "overwhelming love and support for my mother."
Earlier Thursday, The Mount Sinai Hospital spokesman Sid Dinsay confirmed that Rivers was brought there in the morning.
New York City police officials, who spoke on the condition of anonymity because they weren't authorised to publicly name Rivers, said she was taken to the hospital just after 9.30am Thursday. It was unclear why she was visiting the doctor's office.
Rivers' representatives didn't immediately respond to requests for comment.
"They were putting a scope down her throat to check her vocal cords," a source told E! "She stopped breathing."
TV host Billy Bush said on Facebook that he had exchanged texts with Joan's daughter Melissa who asked him to "please pray". Melissa and her son Cooper rushed to be by the star's side.
He wrote: "Praying for Joan Rivers who is in critical condition at Mt Sinai hospital in NY. Texted with Melissa Rivers who said 'please pray.' Already doing that. Joan is beloved around here. A regular guest on Access Hollywood Live she never fails to deliver. She taped her post Emmy special Tuesday in LA and was strong. This is out of nowhere. Come on Joan you have to make it. Just think of all the material. Sending love and prayers."
He later tweeted: "Per Melissa, The mighty @joan_rivers Is in stable condition. That Means her first joke is coming... :)"
According to the New York Daily News, Rivers' assistant, Graham Reed, was overheard saying, "She's not conscious, but she's stable," obviously distraught.
Rivers' representatives didn't immediately respond to requests for comment.
The entertainer has logged a half-century in show business and gave rise to red carpet commentary - and the snarky criticism that often accompanies it.
Her signature red carpet query: "Who are you wearing?"
She continues to maintain a busy schedule, and was to perform a show on Friday at the Count Basie Theatre in Red Bank, New Jersey. That show was postponed because of her hospitalisation.
Rivers spoke at an employee event at Time Inc. in New York on Wednesday night and appeared healthy, practically jogging when she walked in to take her seat, said Shira Blum, an online project manager.
"She seemed totally healthy," Blum said. "She was very energetic, hilarious, funny. And it was such a shock, a surprise to hear the news this morning."
Rivers took questions and said she wakes up every morning and "is thankful that everything works," Blum said.
The host of Fashion Police on E! network, Rivers also presides over an online talk show, In Bed With Joan and co-stars with her daughter, Melissa, on the WEtv reality show, Joan & Melissa: Joan Knows Best?
Her latest book, Diary of a Mad Diva, was released this year.
In 2009, Rivers emerged as the winner of NBC's The Celebrity Apprentice. A documentary, Joan Rivers: A Piece of Work, premiered in theaters in 2010.
A native of New York, Rivers originally entered show business with the dream of a theatrical career, but comedy became a way to pay the bills while she auditioned for acting roles.
"Somebody said, `You can make six dollars standing up in a club,'" she said in 2013, "and I said, `Here I go!' It was better than typing all day."
After proving herself in comedy clubs as a rarity - a woman comedian - Rivers was a smash on her first booking on The Tonight Show Starring Johnny Carson in 1965.
"God, you're funny," Carson told her.
- AP with Daily Mail
DAUGHTER ASKS FRIENDS TO 'PRAY' FOR JOAN
Joan Rivers' daughter has asked friends to 'please pray' for her mother after she was rushed to hospital when she stopped breathing during a surgical procedure.
The 81-year-old was having surgery on her vocal cords at a clinic in Manhattan when she suddenly stopped breathing during the procedure, E! confirmed to MailOnline.
She was rushed to Mount Sinai hospital in critical condition but has now been upgraded to stable after doctors fought to save her life.
'They were putting a scope down her throat to check her vocal cords,' a source told E! 'She stopped breathing.'
The source added that the operation was not a major one though Rivers was sedated throughout. It's unclear what medication was used.
TV host Billy Bush said on Facebook that he had exchanged texts with Joan's daughter Melissa who asked him to 'please pray'. Melissa and her son Cooper rushed to be by the star's side.
He wrote: 'Praying for Joan Rivers who is in critical condition at Mt Sinai hospital in NY. Texted with Melissa Rivers who said 'please pray.' Already doing that. Joan is beloved around here. A regular guest on Access Hollywood Live she never fails to deliver. She taped her post Emmy special Tuesday in LA and was strong. This is out of nowhere. Come on Joan you have to make it. Just think of all the material. Sending love and prayers.'
He later tweeted: 'Per Melissa, The mighty @joan_rivers Is in stable condition. That Means her first joke is coming... :)'
According to the New York Daily News, Rivers' assistant, Graham Reed, was overheard saying 'She's not conscious, but she's stable,' obviously distraught.
E!'s Ken Baker also said that Rivers was now stable after the emergency.
TMZ reported that an emergency call was placed to 911 at 9:39 a.m. New York time.
The caller told emergency services: 'We have somebody in either cardiac or respiratory arrest.'
The drama unfolded at Yorkville Endoscopy on East 93rd street near Third Avenue, police confirmed.
A woman who answered the phone at the clinic this afternoon told MailOnline: 'I don't know what you're talking about, have a great day!'
According to another E! source, Rivers 'had a lot of energy' and was 'cracking jokes' at a Wednesday event in New York to promote her new book.
Similarly on Tuesday, she gave no hint about needed surgery as she taped a special 90 minute edition of her show Fashion Police which aired on E! that same night.
Covering both the Emmy Awards and the MTV VMA's the veteran comedienne's voice did sound raspy but she has become known for her gravelly voice and biting tongue.
The star's no-holds-barred comedy has made her one of Hollywood's mainstays having a career spanning over 60 years.
The often outspoken funny lady - born Joan Alexandra Molinsky - started her career in her native New York performing in comedy clubs across the city and even starred in a play as a lesbian woman with a crush Barbara Streisand in the 1950s.
Joan started to make a name for herself in the male-dominated comedy world as a guest on The Tonight Show from 1965 and then also started landing guest spots on The Ed Sullivan Show.
Taken under the wing of Tonight Show host Johnny Carson as a writer, Joan further developed her biting wit.
Going on to host Saturday Night Live during the Eighties, the iconic star was awarded her show by for The Late Show Starring Joan Rivers - it was this show that led to a bitter fallout with her mentor Carson and he never spoke to her again before his death.
Only this year was Joan's ban from ever appearing on the Tonight Show lifted by Jimmy Fallon.
The comedian would eventually be fired from her Fox show after she challenged executives' decision to removed her husband Edgar Rosenberg as a producer.
Edgar was the star's second husband - her first marriage was annulled after just a few months in 1955 - and he tragically committed suicide three months later in May 1987, Joan blamed the 'humiliation' of Fox's treatment.
- AP, Daily Mail, Bang! Showbiz