According to the Hai Duong Department of Education and Training, watches are not on the list of objects allowed to be brought into exam rooms.
A representative said the policy was the same last year.
The Hai Duong decision stands in contrast to other localities.
Education departments in several localities like Ho Chi Minh City, Vinh Phuc and Ba Ria-Vung Tau will allow examinees to bring their non-smart watches (with only timekeeping functions).
"These items do not contain the possibility to cheat during exams as they do not have the capability to store, emit or receive information," said Le Hoai Nam, deputy director of the HCMC education department.
The representative of the Hai Duong department said several students have used smart watches lately, which can be used to transmit and receive information. For timekeeping purposes, exam sites in Hai Duong all have large clocks, the representative added.
This year, Hai Duong has deployed over 3,250 people to assist 22,000 examinees.
More than one million Vietnamese 12th graders will take the exam, the country's largest, on Wednesday and Thursday.