Greens MP David Shoebridge said the majority of some 13,000 prisoners in NSW are under 24-hour lockdown because of the latest coronavirus outbreak, describing the jails as "human rights disasters".

Terry Givens, whose 42-year-old husband has been in Long Bail jail for 17 months, says prisoners are being denied medical care.

"Our prisoners are broken, fading and they're dying," she said at a small protest outside the Corrective Services office in Sydney on Thursday.

Her husband and other inmates are in the midst of a 10-day lockdown with no contact with the outside world and remain alone in their cells.

Ms Givens is urging the government to uphold its duty of care to all prisoners.

"Since his incarceration in September 2020, he's not even medicated for his condition," she said.

"On top of it the COVID pandemic, the things he's seen in there is stuff you see in a horror movie."

Mr Shoebridge said the deaths of the 47-year-old man and a 48-year-old woman in January at Junee jail had highlighted problems of private companies managing prisons.

Junee prison, one of the largest in NSW, has been run by GEO Group Australia for nearly 30 years.

GEO Group confirmed the deaths to AAP.

"We take pride in our ability to deliver safe and secure correctional environments, with a key focus on the rehabilitation and reintegration of the people in our care," it said in a statement.

"GEO is fully supporting investigations into two recent deaths in custody, of which the causes will be determined in coronial inquests."

Mr Shoebridge said two recent coronial inquiries of the jail had found the firm to be grossly negligent in providing medical care to inmates.

"If they (the NSW government) are serious about the health of inmates and the threat of COVID, they should release them (inmates)."

Australian Associated Press