Joan Rivers is in a "critical condition" after she stopped breathing during throat surgery on Thursday.

According to TMZ.com, the 'Fashion Police' host's heart stopped beating at one point, but it is now believed she's in a stable condition.

Joan's assistant Graham Reed was allegedly overheard saying, "She's not conscious, but she's stable."

However he refused to comment on her condition when a reporter later approached him.

Joan's daughter Melissa, 46, is currently en route to New York and it is believed no drastic medical decisions will be made until she arrives at the hospital.

A family source told the New York Daily News newspaper: "This is not looking good. No big medical decisions will be made until Melissa arrives."

The emergency services received a phone call from the clinic on East 93rd street near Third Avenue at 9:39am (EDT), with the caller saying:

"We have somebody in either cardiac or respiratory arrest."

Meanwhile, Joan failed to mention she was undergoing surgery as she filmed a special 90 minute edition of 'Fashion Police' on Tuesday.