A high school in Miyazaki City, southwestern Japan, is being temporarily closed due to the spread of influenza among a total of 491 people.
City officials say 476 students and 15 employees were confirmed to have been infected with the flu by Tuesday. They say some students began to develop symptoms such as high fever and coughing on May 9.
There have been no reports of serious cases, but the school has decided to close for eight days from Monday.
The school held an athletic meeting at the weekend, and there were reportedly many occasions for students to work in groups, such as during practices for the event.
At a news conference on Wednesday, Miyazaki mayor Kiyoyama Tomonori called on staff and students to take thorough measures against infection such as staying away from school when they feel unwell. He also urged people to ventilate rooms and wear face masks.