1 of 3
Tina Fineberg, Associated Press
A note and flowers are part of a sidewalk memorial for comedian Joan Rivers at the doorstep of her apartment building, Friday, Sept. 5, 2014 in New York. Rivers died Thursday at a New York hospital following complications from surgery. She was 81.

NEW YORK — Further tests are needed to pinpoint comedian Joan Rivers' cause of death, the New York City medical examiner says.

Rivers, who was 81, died Thursday at Mount Sinai Hospital in New York. She had been hospitalized since Aug. 28 when she went into cardiac arrest during a routine procedure at a doctor's office. The New York state health department is investigating the circumstances.

Spokeswoman Julie Bolcer said that the "cause and manner of death" will require further studies.

Rivers' funeral is set for Sunday at Temple Emanu-El; services will be private and no other details were released.

As notables continued to post condolences and memories, fans created a makeshift memorial on the doorstep on Rivers' Manhattan apartment building. Among those sharing their memories of Rivers: Prince Charles, whose 2005 wedding was attended by Rivers.

"Joan Rivers was an extraordinary woman with an original and indefatigable spirit, an unstoppable sense of humor and an enormous zest for life," he wrote in a statement. "She will be hugely missed and utterly irreplaceable."