One man told the South China Morning Post he saw one of the two white bottles, about 750 milliliters, hit the ground about 5 p.m. and the liquid burst out.
"A bottle came down," he said. "It looked like an ordinary bottle of water, and the crowd began to disperse. Then I saw people with red faces and eyes in pain."
Once those splattered realized the liquid was acid they rushed to find water to wash it from their faces and hands, the Post said. Some covered their eyes in pain as they got into ambulances. Others had holes in their clothing or backpacks.
Police said 46 people suffered acid burns but all were released by 10 p.m.
Five hours of searching by police failed to turn up any suspects, the Post reported.
"Judging by the traces and the positions of the two bottles, this is not an accident," Superintendent Annie Fonda of the Kowloon West regional police headquarters said. "We believe someone intentionally hurled them from a height."