More than 500 inmates -- nearly half the population -- of a prison in the US state of Arizona have tested positive for the novel coronavirus, officials said, while at a California prison the virus death toll hit 22.

The Arizona Department of Corrections said Tuesday that 517 inmates at the ASPC-Tucson Whetstone prison "have tested positive for COVID-19."

Those inmates "are currently being housed as a cohort together in separate areas and are receiving appropriate medical care. They will not be allowed back into the general population until they have been medically cleared," its statement read.

The coronavirus has severely afflicted US jails and penitentiaries, home to the world's biggest prison population, which comprises 2.3 million inmates.

Officials are unable to force adequate distancing in crowded cells and face shortages of medical personnel and personal protective gear.

Arizona, population 7.3 million, has reported more than 180,000 coronavirus cases, of which 1,429 are in prisons. Seven of its COVID-19 fatalities came in state prisons.

At least 22 inmates have died of COVID-19 in California's notorious San Quentin prison At least 22 inmates have died of COVID-19 in California's notorious San Quentin prison Photo: GETTY IMAGES NORTH AMERICA / JUSTIN SULLIVAN

California however has reported 51 deaths among prisoners, including 22 in the notorious San Quentin prison just north of San Francisco.

The most recent victim "died August 4th at an outside hospital from what appear to be complications related to COVID-19," the California Department of Corrections said.

One day earlier prison authorities reported the death of a San Quentin prisoner on death row after contracting COVID-19, while five other inmates died between July 24 and 26.

California, population 40 million, has reported more than 524,000 coronavirus cases and 9,700 deaths.

In an attempt to prevent the spread of the virus in the close confines of prisons, since March 11 authorities in the state have released 15,683 inmates who were behind bars for minor crimes or were nearing the end of their sentences.