In Hanoi alone, more than 2,300 cases have been reported since the start of the year across 126 wards and communes, with children under five accounting for 95 per cent of infections, according to the municipal Department of Health.
Hospitals have seen a marked increase in both admissions and outpatient cases, including severe infections with neurological complications linked to the EV71 virus strain.
Health officials said the disease is present year-round nationwide but typically surges between March and May and again from September to October, with annual infections ranging from tens of thousands to around 100,000 cases.
The Vietnam National Children's Hospital in Hanoi has treated more than 700 patients so far this year.
Doctors warned that some parents remain complacent despite EV71 posing a high risk of severe neurological, cardiovascular and respiratory complications if not detected early.
Hanoi has identified kindergartens and home-based childcare groups as high-risk settings, launching disinfection drives and stepping up hygiene and outbreak monitoring.
Parents have been advised to seek medical attention if children develop fever, mouth ulcers or blisters, and to keep infected children at home to prevent further spread.