"The 30-year-old patient is now at the Chengdu Infectious Disease Hospital and people having close contact with him are also isolated for medical observation," the official Xinhua news agency reported.

Aside from the passengers on the man's flight, it said his girlfriend, father and a taxi driver had also been quarantined.

Symptoms

H1N1: At a glance


Deaths: 
Forty-eight confirmed in Mexico, two in the US, one each in Canada and Costa Rica

Countries with confirmed cases: Argentina, Australia, Brazil, Hong Kong, Mexico, the US, Canada, Colombia, Guatemala, Costa Rica, El Salvador, China, South Korea, New Zealand, Israel, Spain, Britain, Germany, Panama, Poland, Sweden, Austria, Switzerland, Denmark, France, Italy, Ireland, the Netherlands, Portugal, Japan, Norway

Influenza epidemics:
Annual influenza epidemics are thought to result in three to five million cases of severe illness and between 250,000 and 500,000 deaths around the world, WHO says

It was not clear from the report which passengers had been quarantined, although Xinhua said the man had developed symptoms of fever on the flight from Beijing to Chengdu.

China's health ministry has urged passengers aboard the last two flights Bao was on to contact the medical authorities as soon as possible.

In 2003, Chinese health officials were criticised for their slow response to the outbreak of the Sars virus which first emerged in China and killed about 700 people.

Following the outbreak of the new H1N1 flu strain in Mexico, Chinese officials promised to implement strict reporting and quarantine measures to prevent the virus spreading to its shores.

Last week, officials in Hong Kong ended the quarantine of nearly 300 hotel guests and staff after a week under medical observation following a Mexican guest being confirmed with H1N1.

But parts of China's response to the new flu strain has been criticised as excessive, with the Mexican government complaining that several of its citizens have been discriminated against solely because of their nationality.

On Sunday, Mexican officials announced they were pulling out of a Shanghai trade fair in protest over China's flu measures, calling the treatment of its citizens unacceptable.