“This one stood out because of what was described to us at the scene and what we found and located just in looking at the scene,” Nanos said.
The sheriff did not offer more details about the cause of their “grave concern”.
Homicide detectives were called to the scene, Nanos said, adding that the involvement of such personnel was not standard protocol. Nanos also said foul play could not be ruled out.
“Miss Guthrie is 84 years old and is not in good physical health,” the sheriff said, but noted her family reported no cognitive issues.
She was last seen at her home after 21:00 local time on Saturday (04:00 GMT on Sunday), Nanos said.
Savannah Guthrie, who hosts the Today show, was not on air on Monday morning.
The programme led with the news and shared a statement from Savannah Guthrie which said: “On behalf of our family, I want to thank everyone for the thoughts, prayers and messages of support.
“Right now, our focus remains on the safe return of our dear mom.”