An "unprovoked attack" in Wanganui was described by a female staying the weekend at a Victoria Ave flat as like being in a war zone.

A young couple and their friend were just about to padlock the entrance gate to the alleyway that led to the upstairs flat where they were staying when a group of about 15 teenagers pushed their way through and attacked them.

They say it was an unprovoked attack by the group that swelled in numbers by up to 30 to 40 people, who left behind knives and bottles they had made into weapons.

The flatmates have been advised by the property owner that they have to pay for the smashed door because it was an act of vandalism, and there was a $500 excess to pay.

About 3am the friends had made their way from a 21st party back to the flat when they were set upon, they told the Wanganui Chronicle.

One of the males, sporting a swollen black eye, said it was a completely random attack when four females from the group of teenagers attacked the young man's girlfriend.

He said she was being stomped on, and he was bashed, as he pulled her up off the ground.

He said they noticed a group of young people on the pavement outside Element Cafe as they walked into the alley.

More teens followed the first group and crowded into the alleyway. The young man told the Chronicle the group were drunk and all wearing similar baggy clothing and peaked caps.

A male who lives in the flat said he was just about asleep when he heard someone calling: "Stop, stop". He watched from his bedroom window then realised he and the four others staying the weekend at the flat, needed to help their friends.

He said they went down the stairs and stood their ground.

But one of them, a visitor, had his head pushed into a water pipe at the side of the alley. The pipe smashed and water sprayed everywhere, which quelled the fight for a short time and allowed the group from the flat to head upstairs to where they thought they would be safe.

One of the males in the flat said he had gone back downstairs to get his friend who he found had been knocked unconscious. He said five of the attackers stomped on his head, then he too was repeatedly stomped and kicked in the head and left with blood coming out of his ears. He now has broken blood vessels in an eye.

He said one of the attackers picked up his friend, who had regained consciousness, and told him to get out of the way and leave.

But then the attackers charged upstairs and kept smashing at the locked door.

"We were really worried they were going to get through the door because they smashed a panel and the door off its hinges."

Another of the attackers climbed up onto a shop verandah to try to get into the flat. In his haste to close the window, it smashed.

Police arrived when the attackers were smashing at the door. Two 17-year old males were arrested and charged with disorderly behaviour, and one for possession of an offensive weapon and resisting arrest.

Officer in charge of CIB Detective Senior Sergeant Dave Kirby said Whanganui police dealt with 21 disorderly offences over the weekend from 4pm Friday to Sunday afternoon.

Details of the incident were posted on the Wanganui Chronicle's Facebook page. Some of the comments were critical of the police, not understanding why they did not shut the incident down sooner.

Mr Kirby was aware that a Facebook thread had criticised the police, but he said they do not have the numbers to attend all incidents. He said police arrived and found a group of intoxicated people shouting abuse.

He said they were following up on CCTV footage and were attempting to identify the people involved in the fracas.

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