The mother of Today show anchor Savannah Guthrie was kidnapped from her home in the middle of the night, police in the US have said.

Officers investigating the disappearance of Nancy Guthrie, 84, say her house is now "a crime scene" as they believe the pensioner was taken against her will. She was last seen at that address in Catalina Foothills, north of Tucson, Arizona, at around 9:30pm local time, on Saturday.

Speaking today, Pima County Sheriff Nanos said: "At this point, investigators believe she was taken from the home against her will, possibly in the middle of the night. Taken against her will includes possible kidnapping or abduction.

"We have an 84-year-old woman who went to bed Saturday night and come Sunday morning, she's gone. We know, at least we believe, and I believe we know, she did not walk out of that home on her own."

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Nancy, whose daughter Savannah has hosted Today on NBC since July 2012, struggles with her mobility, the police sheriff said yesterday. This has led the investigation team to believe a criminal act happened on Saturday night.

Speaking to PEOPLE, Sheriff Nanos added: "She is really just as sharp as a tack. And that too is concerning that here you have this lady who's got all her wits about her, she knows what's going on. So yeah, somebody came into that home, and I believe took her out there without her permission. It was against her will."

Sheriff Nanos added police are working with different vendors to download and review home security footage, adding: "What we have done is we have taken what we believe is biological DNA type evidence, and we are submitting it to our labs, crime labs ... Basically, they'll do a rapid search."

In an Instagram carousel posted on Nancy's 78th birthday, Savannah said her mum is her "everything" and a "model for what a mother should be."

The message reads: "Happy birthday to a mother like no other. My mom Nancy is my heart and my everything and my model for what a mother should be. Thank you, God, for her 78 beautiful years! Happy birthday, mama!!!"

The journalist's fans have, according to police, offered to help with the probe. Sheriff Nanos said their team are thankful for the support, but stressed: "But we really do have an obligation to protect the integrity of this investigation, of any investigation."

Nancy, from Arizona, has at least two grandchildren. She was reported missing after a friend noticed she did not attend church as normal on Sunday morning.