It says a bottle of acid was dropped from above on the crowd in the busy Kowloon area of the city at about 9:30 p.m. (1330 GMT).
Xinhua quotes Hong Kong Cable TV as saying the injured have been rushed to the hospital and police have cordoned off the area.
A series of acid attacks have hit Hong Kong since December 2008 injuring more than 100 people.
Densely populated Kowloon is across the harbor from Hong Kong island. It has narrow streets crammed with snack vendors and shops.
