Japanese schools have been taking precautions against the virus
Health officials in Japan have confirmed the first cases of swine flu in the densely populated capital, Tokyo.
Two schoolgirls tested positive for the H1N1 virus after their return from a trip to New York.
So far, about 250 infections have been recorded in Japan, as a handful of new cases have been reported around Asia.
Health officials stress there have been no deaths from the H1N1 virus in Japan and most cases have been mild.
Nearly 10,250 swine flu cases have been confirmed in 41 countries, the World Health Organization says in the latest update on its website.
The virus is known to have killed 80 people, the vast majority of them in Mexico, where it was first reported.
Tokyo's first known case of swine flu was detected in a girl of 16 who arrived back home on Tuesday from New York.
She had complained of a fever and tested positive for H1N1.
She had a cough and sore throat but was recovering well, said Hideo Maeda, secretary of the city's welfare and health department.
A second girl on the same trip was also infected, officials later told reporters.
Tokyo and the surrounding districts are home to around 36 million people.
Most of Japan's cases so far have been in areas around the city of Kobe to the west where a high school student who had not been overseas was found to be infected on Saturday.
Since then the numbers have risen steadily and more than 4,000 schools have been closed as a precautionary measure.
A 21-year-old Canadian has tested positive for swine flu in Beijing, becoming mainland China's fifth case of the virus, the Health Ministry reported.
The man, who is in stable condition, arrived in Beijing on the afternoon of 16 May aboard an Air Canada flight from Toronto.
Taiwan has also recorded a case of the virus - an Australian doctor who arrived by plane from Hong Kong earlier in the week.
Australia has reported five new cases, including three young brothers, raising the overall number of confirmed infections to six.