They were brought to Long Khanh Town's General Hospital in the province, which borders HCMC, one after another.
All of them developed food poisoning symptoms of vomiting, diarrhea, fever, and abdominal pain.
Doctors diagnosed them with intestinal infection.
Among the patients, 220 are still hospitalized at the Long Khanh Hospital and Dong Nai Rubber Hospital, 88 are self-monitoring their health at home while nine severe cases including children have been transferred to bigger hospitals.
The Dong Nai Children's Hospital has received some of the severe cases, including a 7-year-old who suffered respiratory decline and a 6-year-old boy whose heartbeat and breathing have both stopped.
The banh mi eatery has operated for over 10 years.
A preliminary check has revealed that it does not meet food safety standards, and it has been suspended for further inspections.