Ambulances have been called to treat six people, including one man whose lip was almost severed, after a fight broke out in Newry when a man tried to help another man who had fallen over.
At about 0200 GMT on Saturday two men were walking along Water Street when one fell over.
Another man offered help, but the man refused and a fight began.
A number of men became involved and ambulances were called to attend to six injured people.
Three of the men were treated for slash wounds to their faces. The others received treatment for bruising and minor wounds.
Police have appealed for anyone with any information about the incident to contact them.
SDLP councillor Karen McKevitt condemned the violence.
"Knives were used and people received potentially serious injuries. That is totally unacceptable," she said.
"New Year's night is supposed to be a joyous occasion and one when the town accommodates a large amount of people from all over the north. This has soured that for many.
"Not only did the perpetrators put people's lives at risk but detained vital emergency services and hospital staff who are already overworked due to the bad weather and water crisis."