The first H1N1 swine flu outbreak at a Tokyo school was confirmed Thursday after nine students at Seisoku High School in Minato Ward tested positive for the disease, the Tokyo Metropolitan Government said the same day.

The private school said it would close for a week in an attempt to contain the outbreak. The infected students have not traveled abroad recently and the metropolitan government said it would investigate how they got infected.

New infections were also confirmed elsewhere Thursday, including the first case in Hokkaido, bringing the total number of people infected with the new flu in Japan to 543.

The H1N1 influenza A strain, or "shingata infuruenza" (new-type influenza), has not proved deadly in Japan, and its mild symptoms are treatable with commonly available flu drugs.

The Seisoku students — six boys and three girls — sometimes attended classes in the same room. They developed fevers but are recovering.

Meanwhile, 27 students at a Japanese school in Duesseldorf, Germany, have also contracted the new flu, the school said on its Web site. The school will suspend classes from Saturday to June 19 as instructed by health authorities.