On Tuesday, China's Health Ministry confirmed the country's fourth case of swine flu in a man who recently returned from the United States and Canada.
Chinese officials also say an Italian woman traveling in Tibet was recently suspected of carrying the virus.
The Italian woman was part of 24-member tour group. The ministry says her 23 other fellow travelers are being kept under observation in the Tibetan town of Zhangmu.
A group of foreign tourists were being held on Monday against their will in a hotel in Tibet over swine flu fears in what one angry traveller said was a 'completely inefficient' and lengthy process, fellow traveller Anna Husarska told AFP by phone.
The WHO says the illness has been confirmed throughout the Americas, Europe, Asia and Oceania. The United States has the most confirmed cases, with more than 4,700, followed by Mexico with around 3,100.