A 20-year-old man's hand was nearly severed by an assailant wielding what is thought to be a samurai sword last night in Palmerston North.

Both the man's hands were badly injured by the assailant who had shown up uninvited to a large gathering of young people on Linton Street, Detective Senior Sergeant Craig Sheridan said.

The victim was being treated in Wellington Hospital.

Police were interviewing a large number of people about the attack and it would take several days to piece together what happened, he said.

There had been other reports of fighting and assaults in the area last night, which might be related to this assault, Mr Sheridan said.

About 10.35pm a young man was knocked to the ground on Chelwood St by an unknown assailant. He did not require hospitalisation, Mr Sheridan said.

Shortly after midnight a 15-year-old was hit over the head with a bottle on Pioneer Highway.

He had been with a group of friends when a van load of men pulled over and confronted them, Mr Sheridan said.

One of the men hit the boy with a drink bottle cutting his head. He was treated at Palmerston North Hospital, then discharged.

-NZPA