Ocean Park is to open until midnight on Saturdays in an attempt to shore up visitor numbers.
The theme park, which normally closes at 6pm, will begin the late-night openings from July in the hope of attracting a younger clientele.
The initiative is seen as a move to strengthen the park's competitiveness - it has accumulated losses of $140 million over three years.
Some 5,000 people will be invited to a night carnival with free admission from 6.30pm to midnight on April 28, to test visitors' response to the idea.
It is the second time the park has extended its opening hours. A previous attempt to lure more visitors by opening late on weekdays in July and August 1992 failed.
During the extended sessions, the park will keep its rides open, including the popular mine train at the headland area. The Shark Aquarium and Pacific Piers, from where sea lions can be viewed, will also remain open. Celebrities will be invited to host half-hour performances.
To avoid creating a nuisance to nearby residents, the cable car system, the low-land area with the panda house, and other insect exhibits will not open.