Government spokesman Anucha Burapachaisri said the department has reported a high number of dengue fever cases even before the arrival of the rainy season, when usually cases increase.
The department reported that 17 people had died due to the fever and a total of 19,503 cases were recorded by hospitals nationwide from January 1 to June 7.
Earlier, the department announced that there were 15 deaths and 18,173 dengue fever cases from January to May.
Anucha said the situation is likely to worsen in the rainy season as rainwaters get trapped in various discarded containers, becoming breeding grounds for mosquitoes.
The department reported that the number of cases this year was 3.8 times higher, compared to the same period last year.
The spokesman said that children from 5 to 14 years old was the biggest group of dengue patients and the second biggest group was those who are between 15 to 24 years old.
Dengue cases have been found in 348 districts in 71 provinces.
During the past four weeks, the four provinces of Trat, Nan, Chanthaburi, Mae Hong Son and Satun reported the highest number of cases.
The spokesman said the disease could be fatal for those who were late in seeking treatment at hospitals or those with obesity or other morbidities.
The spokesman advised people to keep their houses clean and tidy and get rid of rainwaters trapped in discarded containers as well as ensure their water containers were closed with lids.
Schools, hospitals, resorts and hotels, factories, temples and government offices are also advised to follow good hygiene practices and be clean to prevent mosquitoes from breeding.