Jump in swine flu cases in Japan

The number of swine flu cases in Japan has risen rapidly - with more than 120 cases now confirmed.

Nearly 2,000 schools and companies have closed, and the government has discouraged unnecessary travel to quell the spread of the disease.

Just four cases had been confirmed in Japan as of Friday - people who had returned from Canada.

The first case in someone who had not been abroad - a 17-year-old student in Kobe - was reported on Saturday.

Call for calm

Japanese media said the new wave in infections would make Japan the fourth-most infected country in the world, after Mexico, the United States and Canada.

None of those infected are thought to be in danger of their lives, officials say, but the government is taking no chances.

"We must be careful, but with quick treatment patients can recover," said Prime Minister Taro Aso. "We must respond calmly and appropriately."

Most of those infected are thought to be students in the Hyogo and Osaka prefectures in western Japan.

Experts believe the virus spread quickly between the two urban areas after high schools in Kobe and Osaka met for a volleyball tournament.

Kobe High School, along with nearly 1500 other schools in Hyogo, has now been closed, and several hundred more are closed in Osaka.

Japan has also established testing centres at airports, and is encouraging high risk groups to wash their hands frequently and wear masks.

Even in the sporting arena, steps have been taken to reduce the potential for infection.

At a national sumo wrestling competition in Tokyo on Sunday, officials sprayed disinfectant on the hands of every spectator as they arrived.

The outbreak has caused alarm in Japan, which with its aging population is exceptionally anxious about flu, the BBC's Roland Buerk in Tokyo says.

People routinely wear face masks on public transport to prevent the spread of coughs and colds.