Triple-murderer William Bell was stabbed "at least once" in the eye in a prison recreation room, police say.
Two makeshift weapons have been recovered and police are planning to lay charges against one of Bell's fellow inmates at Auckland Prison's high-security Paremoremo wing.
"We are looking at charging the offender with some serious charges early next week. We are looking at at least something like wounding with intent to cause grievous bodily harm, possibly attempted murder," said Inspector Gary Davey of North Shore Police.
He said it was not yet clear what had happened but police would continue interviewing witnesses over the next few days.
Corrections Department assistant general manager of operations Bryan McMurray said there was only one other person in the room during the incident.
"We are slowly building [a picture] up - bearing in mind we haven't spoken to Mr Bell yet. We hope to talk to him over the next day or two," Mr Davey said.
The attack took place around 3pm yesterday and police were immediately called, to provide an escort to Auckland Hospital.
"Obviously, because he's a maximum-security prisoner , [and] bearing in mind he's one of our worst offenders, we have contingency plans for this sort of thing," Mr Davey said.
Nearly a dozen police cars packed with armed officers and a police helicopter made up the convoy.
Bell, 29, is serving the longest sentence issued in New Zealand, with a minimum non-parole period of 30 years, for killing three people at the Mt Wellington-Panmure Returned Services Association on December 8, 2001.
The Corrections Department is investigating whether Bell had orchestrated the attack as part of a scheme to escape from prison.
Mr McMurray told Radio New Zealand the prison had been monitoring Bell for months after becoming aware he may have been planning an escape.
"Corrections will not confirm how it gained this information as it would compromise future intelligence gathering capabilities," Mr McMurray said.
He said there was "every possibility" the assault was planned by Bell as part of an escape plan.
The attack came after an article in yesterday's Herald revealed Bell had upset other inmates by boasting about his crime and getting preferential treatment, including extra face-to-face visits, at which he claimed he ate his way through hampers of food.
Corrections Minister Phil Goff dismissed those allegations as rubbish.
Bell is expected to spend another few days in hospital where both Mr McMurray and Mr Goff have said security is very tight.
"He has intense security surrounding the hospital room. Mr Bell is a person, in my view, that should never be released into the community and no chances will be taken with regard to his escape," Mr Goff told Radio New Zealand.
Bell's victims responded with mixed reactions to the attack.
Susan Couch, who suffered horrific injuries in his 2001 attack at the Mt Wellington-Panmure Returned and Services Club, told the Herald she wanted to keep her feelings about yesterday's attack to herself. "I don't believe in revenge or utu."
Tai Hobson, whose wife, Mary, was killed, said: "To hear this news, well ... that's good news."
Mr Hobson said the victims' families had met on Saturday - the sixth anniversary of the killings - for a memorial service.
Asked about the timing of Bell's stabbing - after his boasting in prison and the anniversary - Mr Hobson said: "That's bad luck for him. I'm sure when all the victims hear about it they will be yahooing."
Diane Johnson, whose husband, Wayne, was the first to die in Bell's rampage, said: "In a way I hope he doesn't die - that would be too easy for him."
"I want him to suffer like we have," Mrs Johnson said. "But I will not lose any sleep if he does die."
Bell bashed Mr Johnson with the butt of a shotgun, shot him, then bashed him again.
Carolyn Dunn, younger sister of slain Bill Absolum, said she agreed with other victims' relatives that it was good for Bell to suffer.
"Now he can feel a bit of what we feel," she said.
"Hopefully it is not an easy road for him from here."
Bell's mother, Georgina Tahana, said she had been concerned that another prisoner would attack him "to try to make a name for himself".
"Of course I worried about him. He's my boy - I've worried about him every day since he went in."
Ms Tahana said she wanted to know how her son could have been put in danger, saying she had questions for Corrections "and I want my questions answered".
Prison Services northern regional manager Warren Cummis said the department was treating the attack extremely seriously.
Mr Cummis said it had worked closely with the police to ensure the appropriate security was applied to Bell's escort to hospital.
Bell is serving New Zealand's longest prison sentence - 30 years without parole.
Sensible Sentencing Trust national spokesman Garth McVicar called for an independent review of the way prisons are run, preferably by overseas judges.
He said yesterday's attack showed how bad things had become in jails.
"Prisons have become so politically correct that staff aren't able to enforce rules.
"It has become a recycling place, somewhere prisoners don't fear any more."
- additional reporting: Alanah May Eriksen
* June 2001: Bell is released from prison on parole after serving a five-year sentence for aggravated robbery.
* December 8, 2001: Bell kills William Absolum, 63, Mary Hobson, 44, and Wayne Johnson, 56, at the Mt Wellington-Panmure RSA during a robbery. Susan Couch is severely beaten and left for dead but survives.
* February 12, 2003: Bell is sentenced to 30 years in prison without parole. It is New Zealand's longest sentence.
* Yesterday: The Herald publishes a report on how Bell has got offside with other prisoners by bragging about his crime and the "preferential treatment" he gets. He is attacked in the afternoon.
RILED INMATES ASK VICTIMS' TRUST FOR HELP
Bell is so despised by other inmates that six have complained to Sensible Sentencing Trust about him in the past three months.
The Herald yesterday revealed how one prisoner said Bell got more "contact visits" than they did and claimed to have eaten hampers of food - which are contraband.
"I despise Bell for what he done, for him bragging about his crime, for him bragging about how he gets special treatment."
The prisoner, who described himself as "no saint", said his complaint about Bell to prison management had been ignored, so he turned to the trust even though it was was a victims' rights organisation he was well known to. The trust says his was the latest in a series of letters.
Corrections denies the prisoner's allegations.
A prison source yesterday said that Bell might not have been getting the food, but this did not stop him from "talking it up".
A guard has labelled Bell's maximum-security wing a "holiday camp" run by inmates. Bell and double-killer Graeme Burton constantly threaten staff.