The victims, including children and tourists, were all treated at local hospitals for burns and other injuries and released. The liquid was thrown on them Saturday night near Temple Street, a densely populated district known for its outdoor shops and restaurants in the city's Kowloon area.
Hong Kong has seen a series of similar attacks since December 2008 that have injured more than 100 people.
The suspect, described as a Chinese man in his 30s, was arrested after authorities found him on the roof a nearby building along with caps to the bottles believed to have been used in the attack, said police spokeswoman Michelle Mak.
The suspect has not been formally charged, and the investigation is ongoing, Mak said. She did not say if he was also suspected in other attacks.
Hong Kong leader Donald Tsang said authorities were offering a reward of HK$300,000 ($39,000) for information on the case.
The attack "makes people very angry and sad," Tsang told reporters Sunday.
