"Someone is going to get it."

Those were Luke James Lambert's chilling words to an associate only half an hour before carrying out a frenzied stabbing attack on four strangers in Countdown Dunedin Central in May.

His rampage injured two Countdown staff and two members of the public. Three of them were critically injured and required life-saving surgery.

The 42-year-old pleaded guilty to four charges of attempted murder at the High Court at Dunedin this morning after earlier indicating he would be fighting against any conviction.

The court was told the 42-year-old picked up a packet of four kitchen knives from the shelf of the supermarket about 2.30pm on 10 May and slashed at a supermarket worker who had her back turned to him.

"The blades of the knives were 70mm in length," the summary of facts said.

"The defendant has walked into aisle 7, which is the pharmacy section of the supermarket. The defendant walked halfway down the aisle where he has placed his backpack on the floor. He removed two of the knives from the packaging.

"The defendant, armed with the two knives, walked over to Victim 1 who was working in the aisle stocking a shelf and had her back to defendant. He approached the victim from the left side turning her to face him and using his right hand slashed the victim from the left ear lobe to the chin.

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"As the victim walked back the defendant pushed her and she fell to the floor. The defendant was on top of the victim stabbing her around the head area, causing further lacerations to the chin and left ear. While the victim attempted to defend herself, the defendant continued to stab at the victim's body, causing multiple wounds and injuries to her forearms and hands."

While carrying out the attack Lambert told the victim: "I'm going to kill you".

Another supermarket employee ran over to pull Lambert away from the victim and attempted to restrain him.

As a result Lambert swung the knife at him, stabbing him multiple times including one wound which was so deep it struck the pelvis bone.

A member of the public and another staff member attempted to intervene.

Lambert broke free and then turned his attention to the member of the public and his wife, stabbing them multiple times.

The frenzy only ended when other members of the public, Countdown staff and police officers, including one who was off-duty, restrained him.

They then provided first aid to the four victims until an ambulance arrived.

Their efforts almost certainly saved lives.

Lambert had earlier in the day been shopping at the Countdown store, buying a pie and a soft drink before attempting to buy two cans of beer, which was declined due to a lack of money.

He left the supermarket shortly after 1pm and was later seen in the Octagon by an associate about 2pm.

"The associate described the defendant as 'agitated and pacing around'," the summary said.

"The defendant spoke to the associate and said the 'Doctor wouldn't give him any medication' and that 'someone is going to get it'.

"When the defendant was asked by the associate who was going to get it, he said 'don't worry'."

Police obtained Lambert's medical records after the attack, including a summary of his prescribed medication, and found no evidence he had any medication denied.

When interviewed by officers after the attack he declined to comment.

Lambert will be sentenced in May next year.