Six people who were quarantined after possible contact with Japan's first confirmed swine flu cases were taken to hospital on Saturday after falling ill, local media reported.
They were among 49 passengers isolated by authorities on Friday after arriving at Narita international airport, near Tokyo, with three Japanese citizens who were found to be suffering from the disease, Jiji Press said.
The three, a 46-year-old teacher and two 16-year-old students from the western city of Osaka, tested positive for the A(H1N1) virus after the flight from Detroit.
The six were displaying flu-like symptoms including coughing, high temperatures and headaches, the on-line edition of the Mainichi Shimbun said, adding that they were being treated at three hospitals near the airport.
It was not possible immediately to verify the reports.