An inmate at a maximum security correctional facility in Sydney's west has died after he was allegedly assaulted by another inmate on Friday afternoon.

Officers at the Metropolitan Remand and Reception Centre in Silverwater found the 54-year-old man unconscious in his cell after responding to an alert around 2.15pm.

"The man was taken to Westmead Hospital and later died," a spokeswoman for Corrective Services NSW said. 

Police were called to the facility on Holker Street at about 3.30pm on Friday, after the man was allegedly assaulted by another inmate, a police statement said. 

Corrective Services NSW as well as NSW Police are investigating the incident. 

The correctional facility holds inmates who come directly from court on remand, are transferred from other facilities in NSW while they attend court in Sydney, or are waiting for a vacancy at their centre of classification.

Located about 21 kilometres west of the Sydney CBD, it is one of three facilities part of the Silverwater Correctional Complex.

Police have established a crime scene at the facility and enquiries continue.

A report will be prepared for the coroner.