Two bottles of acid were thrown into a crowd in a popular shopping district in downtown Hong Kong on Saturday, injuring 30 people, police and news reports said.
It was the second such attack in five months in the neighborhood.
Television footage showed firefighters washing off victims' arms and legs before sending them to hospitals for treatment. Some had holes in their clothing.
Hong Kong Cable TV said people in the Mong Kok district had been splashed with acid, though police Superintendent Leung Ka-ming would not confirm what liquid was thrown.
Samples of the liquid will be sent to a laboratory to determine its type, fire services officer So Kam-sang said.
He said 30 people suffered burns but none was seriously injured. Police earlier said an infant was among the injured.
Mong Kok, which means "busy corner" in Chinese, is a shopping hot spot that attracts thousands of local people and tourists on weekends.
On the same street in December, 46 people suffered burns when two plastic bottles filled with acid were thrown at pedestrians. No one has been detained, despite a police reward of 100,000 Hong Kong dollars ($12,900) for information leading to an arrest.
Leung said police would combine the two cases for investigation.
"We will find out whether the two cases were done by the same person as soon as possible," Leung told reporters. "Right now, we do not rule out any possibilities."
The assailant will be charged with intent to cause grievous bodily harm, which carries a maximum penalty of life imprisonment, Leung added.