Participants aged 12 to 75 raced from the Lei Yue Mun region of the Kowloon Peninsula to Quarry Bay on Hong Kong Island, in a course which stretches about 1.5 kilometre.
Thousands of swimmers wearing colourful swimming caps dived into the waters of the iconic Victoria Harbour at 8:30am (0030 GMT), replacing the normal waterway traffic of ferries and cargo boats.
For the next three hours, the harbour was dotted with participants swimming against the stunning backdrop of the Hong Kong skyline filled with skyscrapers and mountains lit up by the morning sun.
For 34-year-old IT engineer Billy Chau, the event was a rare chance to swim in the iconic waterway.
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"I'm very happy to take part in the race because it is difficult to swim in Victoria Harbour and it's hard to have so many people swimming together," he said.
"It will be very memorable for me and my friends, I will think back to this experience when I'm older," added 26-year-old Candy Law, a public relations officer.
Last year's event saw an increase in the enrolment limit from 1,800 to 2,000 as well as the inclusion of a new category to attract the world's top swimmers.
German open water events swimmer Christian Reichert, who won gold at the 2013 FINA World Championships in the five kilometre team pursuit relay, was the winner in the international male category with a time of 15 minutes and 45 seconds.
Poliana Okimoto of Brazil won the international female category with a time of 15 minutes and 56 seconds.
"It's really special, because you have the high buildings everywhere, you have a good view and that's awesome," Reichert said after his victory.
Twenty-year-old Ling Tin-yu, the winner in the 17-34 age category of the past two cross harbour races, repeated his success with a winning time of 18 minutes and 44 seconds.
Hong Kong is one of the world's busiest ports, with more than 410,000 vessels arriving and departing in 2011, according to official figures.