A 23-year-old man was left unconscious in the grounds of a Palmerston North school after being viciously beaten.

The man was unconscious for more than three hours following the attack, which happened at Terrace End School around midnight on Wednesday.

The victim and a 21-year-old man were walking along Ruahine St when they were approached by three men in a car.

Both were punched and kicked, but the 21-year-old suffered only minor injuries.

Detective Shelley Ross said the two victims "vaguely" knew their attackers.

"We're still trying to establish what the groups' associations are with each other," she said.

The 23-year-old man was being monitored in Palmerston North Hospital yesterday afternoon.

The attack began on Ruahine St before progressing down the driveway of the school, Ms Ross said.

Police had no idea what prompted the attack, but were yet to speak to the 23-year-old, who had "significant injuries", Ms Ross said.

He was found unconscious by police at 12.10am and was still unconscious in hospital at 3.30am.

Police only had a vague description of the alleged offenders: two men were dark skinned, one was quite tall and all were believed to be in their 20s.

Police want to hear from anyone who saw a car, possibly a hatchback or stationwagon, or the attackers in the area of Terrace End School between 11.40pm and 12.10am.

Any information can be passed on to Palmerston North police on (06) 351 3600.

- © Fairfax NZ News