A man has been arrested after a 90-year-old woman was allegedly sexually assaulted inside an aged care facility in Victoria.

Police said the woman was asleep in bed inside the St Albans Park facility in Geelong about 4.45am yesterday when a man allegedly broke in.

The woman woke to the man allegedly sexually assaulting her and attempted to fend him off.

Police confirmed today a 23-year-old St Albans Park man had been arrested just after 9am and was being interviewed by police.

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"I understand how much concern an incident like this causes in the community, so being able to make an arrest in just over 24 hours is reassuring," Victoria Police Detective Acting Inspector Mark Burnett said.

"Locating the person responsible has been a significant priority for Sexual Crime Squad investigators ever since the matter was reported to police."

Detective Acting Inspector Burnett yesterday described the 90-year-old woman as a "fighter".

"She was able at one point to activate her personal distress alarm and that's resulted in nursing staff attending," he said.

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The woman and her family will be offered a range of support measures following the alleged sexual assault.

"Our thoughts are with the victim and her family at this time and they will be offered a range of support services," Detective Acting Inspector Burnett said.

"I'd also like to thank the community and the media for all their support in sharing the information we released yesterday."

Anyone with information is urged to contact Crime Stoppers on 1800 333 000.