The incident happened on Thursday night off the island of Hei Ling Chau.
The vessel was en route to Macau. A total of 85 passengers were hurt.
"There was suddenly a loud bang. The ferry was thrown upwards. Then many passengers were thrown out from their seats," one passenger was quoted as saying by Hong Kong's Apple Daily news website.
There were no reports of any people missing, and an investigation is now under way.
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