More than 500 inmates -- almost half of the population -- at a prison in the U.S. state of Arizona have tested positive for COVID-19, local prison officials have said.

According to the Arizona Department of Corrections, 517 inmates at the ASPC-Tucson Whetstone prison have contracted coronavirus and been housed in separate areas and are receiving medical care.

"They will not be allowed back into the general population until they have been medically cleared," the department said in a statement.

The number of COVID-19 cases in the United States surpassed 4.8 million by Wednesday, reaching 4,802,275 as of 3:34 p.m. local time (1934 GMT), according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University.

Among the cases in Arizona, seven fatal infections occured in state prisons.