A Honolulu police officer breaking up an argument in front of a Waikiki business early Saturday morning allegedly was assaulted and injured by a 21-year-old man, who also was injured, police said.

Officers arrested the man around 3:30 a.m. for investigation of disorderly conduct and first-degree assault on a law enforcement officer.

The argument broke out while officers were monitoring the business to deter violent activity, police said. 

Officers escorted the 21-year-old man from the crowd when he allegedly became belligerent and disorderly and turned and assaulted the officer, police said. The officer subdued the man. 

Both the officer and suspect were treated for injuries at a hospital, police said.