The seven include students aged around 15 and an unspecified number of teachers, the ministry said in a statement faxed to AFP late on Tuesday.

The seven were from a 42-strong school tour group who were all quarantined upon arrival in the central Chinese city of Yichang on Thursday last week after four of them showed symptoms of the A(H1N1) virus, the ministry said.

All 42 remained in quarantine. Earlier reports in US media identified the students and teachers as coming from Pacific Ridge School in California.

On Tuesday, Chinese health authorities announced that there were 237 confirmed cases of the virus on the mainland.

China confirmed its first case of the illness - which has killed more than 160 people worldwide - on May 11, but it has so far recorded no deaths. -- AFP