The South China Morning Post quoted the police as saying the attacker stopped to talk to a handbag seller, whom he accused of having an affair with his wife.
After exchanging words, Chau pulled a bottle from his bag and splashed the man. The liquid also burned the vendor's wife who was at the stall, said the news website.
Nearby shoppers were also splashed in the attack.
A female tourist told Hong Kong radio that she saw several people wrapped in bandages taken to ambulances on stretchers.
"I just saw three people being wheeled out, two women their faces covered [in bandages], body covered, and then also one elderly man with his body covered but not his face."
Police said Sunday's incident was unrelated to three similar previous attacks in the same neighbourhood which between them have injured some 100 people.
Those incidents were caused by someone hurling acid from a building and local authorities installed security cameras in the district to try to find who was responsible.
However no one was arrested.