Tokyo officials are trying to contain an outbreak of dengue fever in the city, the first in nearly 70 years.
The outbreak, which is thought to have originated in one of the city’s largest, most popular parks, has so far infected 34 people, according to public broadcaster NHK.
None of the victims are thought to be in serious danger. Officials believe they were bitten by mosquitoes carrying the virus, which is not transmitted between humans.
Health workers have sprayed insecticide throughout Yoyogi Park and set traps in a bid to lure the insects and identify the source of the infection.
Signs around the park, which is normally crowded with families, joggers and bicyclists, are warning people to wear long sleeves and pants and to use repellants to keep mosquitoes away.
The city's government has set up a hotline for queries about the virus and has received hundreds of calls from across Japan, according to the local media.
Dengue Fever is normally found in tropical and subtropical areas of Asia, Latin America and Africa. The virus causes a high fever and severe joint pain and in some cases heavy bleeding and death.
There are no vaccines or drugs to treat it.
The number of infections has accelerated quickly in recent years and broken records across Asia, driven by climate change and wetter, more humid weather, say scientists. The virus killed dozens of people in Malaysia earlier this year.
It strikes down around 200 Japanese holidaymakers abroad a year but the Tokyo government says nobody had been infected in Tokyo since 1945.
Japanese scientists have blamed an exceptionally wet summer in Tokyo and warming temperatures, which they say has pushed the Asian tiger mosquito, which carries the virus, further north.
Japan’s health minister Norihasa Tamura said that an epidemic in the world’s most populated metropolis was highly unlikely. “It’s not as if mosquitoes carrying the virus are always in Japan, so please do not panic.”
Many parents are keeping their children away from the park, however, until the outbreak is contained. “I read about it online and it’s scary,” said mother-of-two Yasuko Ishida, who lives near Yoyogi. “I’m sure it won’t spread but it’s better to be safe than sorry.”
Experts say Japan’s cooler autumn and winter will kill off the mosquito, but they warn the outbreak could be a sign of things to come in warmer areas.