Two teenage students in Tokyo have been confirmed to be infected with the mosquito-borne dengue virus.
Tokyo officials say the two, a girl and a boy, attend the same school.
The officials say the two visited Nara and Kyoto, major sightseeing cities in western Japan, on a school excursion from September 18 to 20.
The two showed symptoms such as high fever after they returned to Tokyo, and their infection with the dengue virus was confirmed on Thursday last week.
They were hospitalized, but later recovered, and were discharged.
Dengue is a viral disease that causes humans high fever, headache and other symptoms. The virus cannot be transmitted between humans.
None of the students had traveled abroad during the two weeks immediately before they developed symptoms.
The officials say the two cases are the first dengue infection in Tokyo since 2014 for people who have not travelled abroad just before the infection was confirmed.