A violent attack on a Hamilton dairy worker which ended in two of his fingers cut off with a machete shows the "extreme level of violence" offenders will go to, police say.

The worker at Irvine St Dairy was attacked by four men, one of whom was wielding a machete, as the robbers stole cigarettes and tobacco on Saturday morning.

The man lost a finger and thumb in the violent attack.

But the dairy's owner, Puneet Singh, says it could have been much worse.

"He was begging to them 'don't kill me, don't kill me'. He was saying that again and again, and he was saying the robbers were trying to kill him.

"The robber targeted my worker's head. He just brought his hand in between and that caused the cut to his fingers."

Singh says his worker's fingers have been reattached, but it's unclear whether full function will return.

The man also suffered defensive injuries to his other hand, though they are not as severe.

The man is also deeply traumatised, says Singh.

"He's still in trauma.

"They attached his fingers back but they are not sure at the moment how they will perform. The surgery took around eight hours to put the fingers back and he is still very scared. He is still thinking about what has happened."

Both Singh and the worker just want the men responsible caught.

In a media conference, Detective Senior Sergeant Kristine Clarke says the incident shows the "extreme levels of violence" offenders are willing to go to.

She says the violence, in which a dairy worker lost a finger and a thumb, is distressing for everyone involved.

"It's really really disturbing - it's really taking this type of thing to another level. The gratuitous violence that was involved is distressing obviously to the victim and the victim's family and to the wider community and to the police officers that are dealing with it."

Clarke says they are determined to hold the offenders to account.

Police are waiting for the victim to recover further before questioning him about the attack.

But she says people will know who the offenders are - and it's up to them to take a stand.

She says police are constantly reviewing their processes and what can be done to prevent such attacks.

"We are doing the best we can to prevent this."

Police want witnesses to come forward.

"Police were called to the scene about 7.30am, and on arrival discovered a man outside the premises with a serious injury to his hand. First aid was immediately administered, and he was transported to hospital, where he remains in a stable condition.

"We understand this is a distressing incident that will cause a great deal of concern to the wider community.

"Police are committed to finding those responsible and holding them accountable, and we are following several lines of enquiry. We would like to hear from anyone who may have witnessed the incident or events immediately after, or who has information about those involved.

"We would also like to hear from anyone who has private CCTV in the immediate area or surrounding streets, which may have captured footage of use to the investigation."

Singh says the government needs to do more to keep retailers safe.

"There should be harsher penalties. If they don't have any consequences when they are caught ... they are going to come back and do it again.

"Until we put them under pressure and give them harsher penalties this is going to keep repeating. The government needs to change the law and give more power to police, so they know there are consequences."

On Saturday, Singh estimated the men stole between $15,000 and $20,000 worth of tobacco products.

-RNZ.