Detective Superintendent Heather Pearson, of North Yorkshire Police said:
As a result of the incident a criminal investigation is underway. Officers are deployed to support the 83-year-old woman who is being cared for by family members.
"A number of enquiries are ongoing including tracing people who can assist.
"Detectives would like to speak to anyone who can assist in establishing a picture of the events leading up to the assault and ask that they contact York CID as soon as possible."
Any witnesses are being asked to contact North Yorkshire Police on 101.
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Kerrie Gosney brings you Sunday night's forecast
Cold with wintry showers overnight and on Monday.
Cold air from Canada will turn showers wintry overnight into Monday morning. Snow could settle over higher routes. Icy patches possible