Savannah Guthrie has accepted her missing mom Nancy Guthrie is "with God" but she "needs to know" what happened to her.

The TV presenter's 84-year-old mother disappeared from her Arizona home on February 1 and police have been treating her disappearance as a kidnapping - now Savannah has admitted she believes Nancy is no longer alive after receiving a message from a higher power.

During an interview with her Today show colleague Hoda Kotb, Savannah cried as she explained: "Early on, I felt that I heard, one of the very few times in my life, I did hear God speak to me.

"As I said to myself: 'I can handle anything. I just can't handle not knowing ... I have to know'. And I heard a voice and it said: 'You do know where she is. She's with me.'

"So whether she's on this Earth still or whether she's in Heaven, I know where she is. I know who she's with. But we need to know. "

In the second part of the interview broadcast on the Today show, Savannah also described the moment when she left Arizona to head home to New York as the search continued - revealing she wept as she looked out of the airplane window overlooking the desert her mom "loved".

She said: "I looked out the window of the airplane and just thought: 'Where are you?' That desert, that beautiful desert that she loved. 'Where are you? How could I leave you?'"

However, Savannah insisted she learnt a lot about dealing with grief from her mom after their family was rocked by the loss of the TV star's dad.

She said: "My mom taught me a lot about grief. Our family knows grief. My father passed when I was 16 years old. He was only 49. It was a shock.

"And I remember my mom saying in those early days when daddy died, like: 'You have to get up and decide and do. Just decide and do ... '

"I always remember that so I'm just trying to decide and do. Get up and decide and do every day. I've felt terrible grief and I've felt unfathomable love and comfort ... She showed us how to survive the unimaginable."

The Pima County Sheriff's Department (PCSD) launched an urgent search for Nancy after she failed to show up for a church service on 1 February, the day after her relatives had dropped her home.

Investigators believe she was kidnapped overnight, and have obtained surveillance footage of a masked man at her door.

Earlier this month, Pima County Sheriff Chris Nanos admitted that investigators believe they know the motive behind the kidnapping, but didn't offer any details.

He told NBC News: "We believe we know why [the kidnapper] did this and we believe that it was targeted, but we're not 100% sure of that.

"I think day one, we had some strong beliefs about what happened, and those beliefs haven't diminished."

Savannah and her family are offering a $1 million reward for information that leads to Nancy's "recovery". They are also planning to donate $500,000 to the National Center for Missing and Exploited Children to help other families with missing loved ones.