Data from travel platform Mustgo, which partners with 100 hotels in the south central beach town, showed two- and three-star hotels in the downtown fully booked for the week.
The four-star Anya Quy Nhon reported no rooms on Friday and other high-end hotels are almost full.
The fourth season of VnExpress Marathon Quy Nhon will take place on Sunday, attracting more than 10,000 runners.
Return air tickets from Hanoi, HCMC to Quy Nhon cost from VND3 million ($130) per person.
Quy Nhon has emerged as a rising star on the Vietnamese tourism map thanks to its long, sandy beaches and crystal blue waters.