The identity of a high-profile criminal who lashed out at a prison guard after being denied access to a phone is being kept under wraps.

The Corrections officer suffered bruising and swelling to his head and face during the assault on Monday, acting prison manager Yvonne Fuller said.

The guard was taken to hospital but had since been discharged. Police were investigating the assault.

It is understood the prisoner - who is a high-profile violent criminal - attacked the officer as he was refused phone time.

Ms Fuller said Corrections was unable to release any details of the prisoner involved as he was due to appear in court in the coming weeks on unrelated charges. Identifying him now could prejudice that case, she said.

It is the second assault on a prison officer at Hawke's Bay Prison this year.

A Corrections officer, in his late 40s, was violently attacked in July, and suffered a fractured eye socket and a deep cut to his cheek.

A month earlier, a Rimutaka Prison warden suffered serious head injuries when going to the aid of a prisoner who was assaulted by a group of inmates.

In 2010, Waikato prison guard Jason Palmer, 33, died after being punched by prisoner Latu Kepu.

A posting on the Corrections Association New Zealand Facebook page asked when Corrections staff would be able to defend themselves like the police.

"They carry batons, pepper spray and tasers for when they come across these people. We deal with them every day and we suffer what our boss calls unpredictable attacks."

Ms Fuller said Corrections officers worked in a tough environment because prisoners were volatile and unpredictable.

- © Fairfax NZ News