NSW prison guard charged over 'affair'

A prison guard will face court over claims she had a relationship with an inmate and passed on sensitive information to prisoners at a jail on NSW's mid north coast.

The 34-year-old officer was allegedly sexually involved with Sione Penisini who is serving a 36-year sentence at the Kempsey facility for the murder of Senior Constable Glenn McEnallay in 2002.

Police began investigating the allegations last week following a referral from Corrective Services NSW.

They arrested the woman at a home in Smithtown on Thursday and charged her with misconduct in public office and larceny.

The offences can attract a fine and up to four-and-a-half years in jail.

Police allege that between July 2 and 22 the guard engaged in an intimate relationship with an inmate, passed "sensitive information" to prisoners and failed to disclose a conflict of interest.

She is also accused of collecting a parcel from a post box in June that wasn't addressed to her and keeping the package.

Acting Assistant Commissioner Stuart Smith on Friday said he was "appalled" by the behaviour.

"The extent or the outcomes that may come from passing on information in a jail system could be critical," he told reporters in Sydney.

"It could result in an injury or death to an individual, you never know."

Investigators are trawling through an "extensive" amount of surveillance material from the prison and haven't ruled out further charges, he said.

The woman, who has since been suspended, was granted strict conditional bail to face Kempsey Local Court on August 20.

The NSW government last week announced a special task force to investigate inappropriate relationships between guards and inmates over the past decade.

NSW Corrections Minister David Elliott said he was appalled by the recent allegations and suggested there were "cultural issues" within the system.

Former NSW Police assistant commissioner Mark Murdoch will lead the review.