The National Paediatrics Hospital is currently handling 69 cases of Japanese encephalitis, compared with five handled by the National Hospital for Tropical Diseases.
Phu said the diseases were caused by different kinds of virus strains including the Japanese encephalitis virus. Patients often suffered brain damage from the disease resulting in long-term damage or fatalities, he said.
Children under 15-years-old were especially vulnerable to the disease, added Phu.
The disease appeared at the beginning of the year and has seen a steady rise in the summer months.
The vaccine against Japanese encephalitis was adopted into the National Immunisation Programme in 1997.
After an initial roll-out in some high risk provinces and cities the vaccine was gradually expanded to more localities.
Last year the vaccine was used in 60 provinces and cities and was supplied free-of-charge to children under-five-year-old in all 63 provinces and cities.
The health ministry prepared 4 million of doses of Japanese encephalitis vaccines this year, an increase of 1.7 million doses compared with the previous year.
It also assigned experts to check and advise on disease prevention in different localities. Information on the disease has also been disseminated to raise awareness.
Experts from the health ministry warned that to prevent Japanese encephalitis, residents should monitor hygiene levels at home and at work.
Livestock cages should be placed away from houses and cleaned regularly to prevent mosquitoes from breeding.