Hong Kong leader Donald Tsang condemned the attack, saying it was "cold-blooded and evil" and the assailant was "scum of the society." Investigators have posted a 900,000 Hong Kong dollar ($116,097) reward for information leading to an arrest.
Police were reviewing footage from surveillance cameras for clues who was behind the third such attack in the neighborhood six months.
On the same street last month, 30 people suffered burns when two plastic bottles filled with acid were thrown down into a crowd.
Another 46 were injured in a similar attack in that neighborhood in December.
Residents in this city of 7 million mostly went about their business Tuesday, seemingly unfazed by the latest attack. But in Mong Kok - which means "busy corner" in Chinese and is a shopping hot spot that attracts thousands of people daily - some shoppers were staying away.
"I thought the attack would be stopped, but it happened again," one of the victims surnamed Leung was quoted as saying in Hong Kong's Ming Pao Daily News. "I always go to Mong Kok, but from now on I'll never go to that area again."
Leung suffered burns on her neck and back, according to Ming Pao.
The attack dominated the headlines in the Chinese territory.
Several newspapers ran photos showing victims washing off the acid on the roadside.
Police superintendent Edward Leung was quoted as saying in the South China Morning Post that it was possible the same person had carried out all three attacks.
Leung said in a radio interview Tuesday that officers were reviewing surveillance footage taken by cameras recently installed to monitor the area of the attacks. But he said it wasn't immediately clear whether the assailant would be identified because some of the images are too dark.
If convicted, the assailant would be charged with intent to cause grievous bodily harm, which has a maximum penalty of life imprisonment, Leung said earlier.
NEW YORK AND TRI-STATE AREA NEWS
REPORT A TYPO || GET WIDGET
VIDEO: Eyewitness News || VIDEO: ABC News || VIEWER PHOTOS & VIDEOS ||