Direct flights from India have been suspended since there were few or no passengers, Bui Quoc Thai, director of the Kien Giang Province Department of Tourism, said as cited by Voice of Vietnam newspaper.
Charter flights from Taiwan and Hong Kong have been canceled, he added.
Only flights from South Korea, Malaysia and Thailand continue to operate.
In April foreign visitor numbers plummeted by 27.3% from the previous month to 47,725, according to the department.
Tourism officials blamed this on the global economic situation and inflation.
Well known for its long, sandy beaches with turquoise waters and dense forests, Phu Quoc is a popular holiday destination for both Vietnamese and foreign tourists.
It is also home to a marine sanctuary and a national park popular with trekkers.