Warning posters on a closed gate of Tokyo's Yoyogi Park, Friday. Pic: AP.

A popular park in downtown Tokyo has been closed temporarily after dozens of cases of dengue fever were contracted by people who visited the area.

Health minister Yasuhisa Shiozaki on Friday urged the public to remain calm, but said all local governments would be given guidelines on how to identify and handle dengue, which is spread only by mosquitoes.

Tokyo’s popular Yoyogi Park was closed off this week as government workers sprayed the area with insecticide. Officials have also begun trapping mosquitos in the area in an attempt to determine how many are carrying the virus.

Tokyo residents have been advised to avoid the area and wear long sleeves and trousers. Shiozaki said the virus could spread “explosively”.

Dengue is endemic in much of tropical Asia and there are dozens of cases brought back to Japan each year, but health officials recently confirmed the first locally transmitted cases in 65 years. As of Thursday, the number of infections was reported at 55. There have been no deaths so far, but a number of victims remain in hospital.

Dengue cases in Asia often spike at this time of year, when warm, wet weather promotes a sharp increase in mosquito populations.

In Malaysia, a virulent strain of the virus had infected 68,144 people and claimed 131 lives as of August 30, about four times higher than last year.

According to the World Health Organization (WHO), about 40 percent of the world’s population lives in areas where dengue is prevalent:

Today, dengue ranks as the most important mosquito-borne viral disease in the world. In the last 50 years, incidence has increased 30-fold. An estimated 2.5 billion people live in over 100 endemic countries and areas where dengue viruses can be transmitted. Up to 50 million infections occur annually with 500,000 cases of dengue haemorrhagic fever and 22,000 deaths mainly among children.

Dengue causes symptoms including fever, severe joint pain and headaches. There is no treatment, and some of those infected can suffer from severe and life-threatening bleeding.

The Bangkok Post reported Wednesday that, “French drug maker Sanofi, developing the first vaccine against dengue fever, said its product reduced disease cases by 60.8% in a its large-scale and final clinical trial.” The vaccine is expected to go on the market in the second half of 2015.

Additional reporting from Associated Press