San Francisco Sheriff's Department and city police investigators were treating the area of San Francisco General Hospital where the body was found as a crime scene, the San Francisco Chronicle reported.
Hospital spokeswoman Rachael Kagan said the body was discovered by a hospital employee about 10 a.m. PDT in an exterior stairwell on the fourth floor, the newspaper said. She said she didn't know if the body was that of Lynne Spalding, 57, who was being treated for complications from an infection when she vanished from the hospital last month.
It wasn't known how long the woman had been in the stairwell or how she came to be there. The stairwell is used as a fire escape.
"It's very concerning," Kagan said. "We're distressed and don't know what happened. It's our top priority to find out."
A spokesman for Spalding's family said they were waiting for more information from authorities.
"We continue to live in hope that Lynne is out there alive," family spokesman David Perry said, adding he found it "horrifying" and "deeply disturbing" that a body had been found in a hospital stairwell.
"Hospitals are places for healing and certainly San Francisco General knows a lot about healing," he said, "but what is happening here today is very distressing, and although we hope that our friend and our colleague Lynne Spalding will come back to us alive and healthy, we're very concerned about this, and we're awaiting either identification or confirmation that this isn't Lynne."
Spalding, a native of England, was last seen at the hospital the morning of Sept. 21. She had entered the hospital two days earlier, Perry said.
Kate Middleton recycles dress at movie premiere
Jordana Brewster on Paul Walker: 'He was an enormous presence in my life'