TOKYO - Japan announced on Saturday its first confirmed cases of the new strain of flu -- a teacher in his 40s and two male teenage students who had spent time in Canada.

The global spread of the virus has kept alive concern over a possible pandemic, although scientists say this strain does not appear more deadly than seasonal flu.

The three Japanese had returned to Japan via Detroit on Friday after spending time in Canada, Health Minister Yoichi Masuzoe told a televised news conference.

All three were in hospital and the teacher was being given Tamiflu while the two students' fevers had subsided, he said.

Another 49 passengers who arrived on the same plane will stay in a separate facility for observation for 10 days, while all passengers on the plane were urged to pay close attention to their health for the same period and contact health authorities if they suffered any symptoms.

The new H1N1 flu has killed its first patient in Canada, making it the third country after Mexico and the United States to report a death from the virus that has sickened more than 3,000 people in 27 countries.

Japan has been checking passengers arriving on flights from the United States, Mexico and Canada and will keep doing so, but Masuzoe noted that such measures had their limits.

I want to ask everyone to respond calmly and coolly, Masuzoe said.

We managed to stop these (cases) at the border ... So I think one can evaluate the steps positively to some extent, Masuzoe said. But we need to take crisis management measures thinking that the spread inside the country is a matter of time.

Japan has compiled detailed guidelines for a new flu outbreak, including possible closures of schools and businesses, but officials have stressed the need to respond flexibly.

We want to decide on whether to strengthen measures or relax them by watching the situation, Masuzoe said.

Health officials have been advising the public to gargle and wash their hands frequently and consider wearing face masks -- popular in Japan anyway for cold and hay fever sufferers.