Hong Kong police said on Monday they were investigating a fourth acid attack in less than a year in one of the world's most densely populated neighbourhoods.
Eleven people suffered burns Sunday when a man flung liquid at a market trader in the southern Chinese city's bustling Mongkok district, police said.
Mongkok, a haven for shoppers looking for cheap clothes and electronics, has one of the planet's highest number of inhabitants per square kilometre (mile).
Forty-six people were injured in December last year when two bottles of corrosive liquid were tossed from a building into the street. Similar attacks in May and June injured more than 50 people.
A reward of 900,000 Hong Kong dollars (115,000 US) was offered to anyone who could help find the culprit, but so far no one has been arrested.
The latest incident prompted fears among bystanders that it was a repeat of the earlier attacks, although police said there was no evidence of a link.
Detectives were investigating claims that the attacker believed the stall owner was having an affair with his wife, a police spokeswoman said.
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