The group of tourists ate a buffet breakfast at Diamond Bay Condotel Resort in Nha Trang of Khanh Hoa Province on Tuesday that contained 30 dishes and served around 600 customers, including Vietnamese, Russians and Chinese.

Several hours later, many began suffering stomach pain, vomiting and diarrhea and were sent to the emergency room at a local hospital, said Le Tan Hung, deputy director of the provincial health department.

All victims are now in stable condition and were discharged from hospital on Wednesday.

The health department said it had collected food samples from the resort to determine the cause of the food poisoning, results to be announced Thursday.

Nguyen Ngoc Hoang, general manager of the resort, said the buffet lasted from 6 a.m. to 10 a.m. Early in the afternoon, he received information that a group of Chinese tourists were hospitalized with food poisoning symptoms while many others remained normal.

"We are not clear as to the cause, but joined local authorities to review the stages of food preparation," Hoang added.

Nha Trang has long been a hotspot among Chinese tourists, accounting for the majority of total foreign arrivals in Khanh Hoa. Last year, Khanh Hoa province welcomed two million Chinese, up 41 percent from a year ago, according to official data.

Food poisoning occurs frequently in Vietnam, especially after meals at school and factory canteens.

There were 84 cases of food poisoning recorded in 2018, affecting 3,174 people and killing 11. In 2019, 63 cases of food poisoning have been recorded, affecting 1,723 people and causing nine deaths.