Phu Quoc Island has emerged as a new entrant, replacing Hoi An in the top 5.
This shift underscores Phu Quoc's growing popularity, likely driven by its stunning beaches and increased international flight connectivity from Seoul, Agoda said in a statement based on its booking data between January and June.
Agoda's rankings also matched tourism statistics for the first half of the year.
Phu Quoc received nearly 4.5 million tourists between January and June, up 33% year-on-year.
The number of foreign tourists to the island reached nearly 900,000, a 76.7% year-on-year increase, and close to this year's 1-million target.
A number of Asian celebrities like Chinese actor and martial artist Vincent Zhao, and Miss Hong Kong 2011 Rebecca Zhu recently visited Phu Quoc, further boosting its appeal.
The island has received multiple accolades from global travel publications. Recently, it ranked third on Travel + Leisure's list of the 10 best islands in the Asia-Pacific, behind only Bali and Koh Samui.
Last year, Phu Quoc was voted the world's second most beautiful island by Travel + Leisure readers, just after the Maldives.