Key Points:

The man who murdered Auckland teenager Liam Ashley in the back of a prison van has been involved in another transportation attack - this time using a makeshift knife against a prison officer in an apparent escape bid.

George Baker, 28, is serving a sentence of at least 18 years for strangling and then stomping on the 17-year-old while the pair were being transported in a prison van in August 2006.

Last night, the Corrections Department told the Herald that on Saturday night, while prison staff were escorting him from Auckland City Hospital to Paremoremo maximum-security prison, Baker used "a small piece of metal he had concealed on himself internally".

The department said privacy reasons prevented it from revealing why Baker had been treated in hospital. However, the Herald has learned his injuries were self-inflicted.

Corrections is conducting a review of the incident which will look at how Baker came to be in possession of the makeshift knife.

Prisoners are known to "self-harm" under the belief that they will find an opportunity to escape while seeking medical treatment.

Many cases are treated at the prison's medical centre but others requiring specialist treatment are taken to outside medical facilities.

In response to the incident, Corrections northern assistant regional manager Jeanette Burns said: "Staff acted immediately and appropriately. They restrained the prisoner and removed the weapon from him. One staff member received a minor cut to his finger, he was seen by medical professionals as soon as was practicable."

A Corrections spokesman said "internal charges" against Baker had been laid.

Penalties for prisoners include loss of privileges and could also involve a period in "confinement".

North Shore police area commander Inspector Les Paterson said police had been notified of the incident.

"It is unlikely however the police will be taking the matter further as the Corrections Department have ample powers to discipline prisoners following low to moderate level incidents."

Beven Hanlon, president of the Corrections Association which represents prison officers, was not able to be reached for comment.