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Police have arrested a 16-year-old after a samurai sword attack nearly severed a man's hand outside a Palmerston North party.

The youth, from Bunnythorpe, near Feilding, was arrested yesterday and charged with wounding with intent to cause grievous bodily harm.

He would appear at a special sitting of Palmerston North District Court this morning, said Detective Senior Sergeant Craig Sheridan.

"The samurai sword used in the attack has been recovered from a local address. It is approximately one metre in length," Mr Sheridan said.

The 20-year-old victim spent most of yesterday having surgery to reattach his hand after the attack outside a party on Saturday night.

His left hand was almost severed and the other hand badly damaged in the attack.

It is not yet known if the surgery will be successful.

Police have spoken to 20 witnesses to the attack and will continue to interview them this week.

Palmerston North police were also investigating two bottle attacks on Saturday night, which appeared to be unrelated to the sword incident.

About 10.30pm a man was struck to the ground in an unprovoked attack by three people armed with bottles in Chetwood St. He did not require hospital treatment.

A 15-year-old youth was also attacked outside the BP service station in Pioneer Highway about midnight, Mr Sheridan said.

A light coloured van containing about eight males pulled up and one of them struck the youth in the head with a bottle, cutting him.

The victim was treated at hospital and released.

"This appears to be a case where a group of young men are cruising the streets looking for trouble. I consider it likely that this isn't the first time they have behaved in this violent manner," Mr Sheridan said.