Australian police have confirmed that a "frail" 95-year-old grandmother is barely conscious days after being tasered by an officer as she slowly approached towards him on her walking frame while holding a steak knife.

"We are very concerned about what occurred the other day. And that's why we have the investigation," New South Wales state police assistant commissioner Peter Cotter said on Friday, alluding to a previously announced probe.

Claire Nolan, a "much-loved lady", was in critical condition following the confrontation at her nursing home on Wednesday, Cotter told media in Sydney.

"At the time she was tasered, she was approaching police but it's fair to say at a slow pace. She had a walking frame but she had a knife."

Officers were sent to Yallambee Lodge in southern New South Wales after being alerted by nursing home staff that a woman was "armed with a knife", police said in a statement.

Paramedics and police had urged Nolan to drop the serrated steak knife in a conversation lasting "a number of minutes" before she moved toward them, prompting one officer to fire his taser at her, Cotter said.

She then fell backwards and struck her head on the ground, according to police.

'Confronting' video images

The duty status of the police officer who fired the Taser is "under review", according to the police.

It took days for police to confirm they had tasered the aged-care resident, whom local media described as a great-grandmother with dementia.

Police body cameras had captured "confronting" footage of the incident, which would form a central part of the investigation, Cotter said, adding that the footage is not being released for the time being.

On the day of the tasering, police said only that Nolan had "sustained injuries during an interaction with police".

In his recent address, Cotter said the "injury that she suffered as a result of hitting her head on the floor has rendered her bedridden at the moment," adding that Nolan is still in the hospital and "remains in and out of consciousness."

A team including homicide squad officers had opened a "critical incident investigation", including "the discharge of a taser", police said. The probe is subject to independent review.