Hanoi topped the list, followed by Da Nang and Da Lat, based on accommodation searches for check-in dates from Aug. 29 to Sept. 3.
This year Vietnamese people enjoy a four-day break for the 80th National Day, from Aug. 30 to Sept. 2.
Phu Quoc is favored for its long, sandy beaches, high-end entertainment complexes and ancient temples.
The island has become a bright spot of Vietnam's tourism industry.
It received 5.2 million visitors in the first seven months of this year, a 31.8% increase compared to the same period last year.
Tourism revenue from January to July increased by 93% year-on-year to VND24.8 trillion (US$947 million), according to a report from An Giang Province Department of Tourism.
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, it was voted the world's second most beautiful island by Travel + Leisure readers, just after the Maldives.