Japan said on Sunday that 20 more people had tested positive for swine flu, bringing the total number of cases to 32 amid fears the virus has a foothold in the west of the country.
The latest group of flu sufferers included 18 high school students in Osaka prefecture and the city of Kobe in neighbouring Hyogo prefecture, where eight students were already ill from the virus, a health ministry official told AFP.
A college student in his 20s and a teacher in his 40s, both in Kobe, also tested positive for A(H1N1) influenza, he said. "Now the number of cases of domestic infection has risen to 28," the official said.
Four other Japanese a school teacher and three students who flew to Tokyo from Canada via Detroit contracted the virus overseas earlier this month and have since recovered.
"We quickly need to collect information on the current infection," said Chief Cabinet Secretary Takeo Kawamura, the top government spokesman.
"We are studying how to prevent the spread of infection," Kawamura told reporters, adding that the cabinet would hold an emergency meeting on Monday to discuss the issue.
Prime Minister Taro Aso has called on the country to remain calm.