A Chinese man returning from studying at a U.S. university has become the first suspected case of swine flu in mainland China, the Health Ministry said Sunday.

The ministry identified the patient as a 30-year-old student surnamed Bao studying at an unspecified U.S. school.

If confirmed, Bao's case would be the first in the mainland and China's second in the global outbreak. The Chinese territory of Hong Kong earlier reported a case of swine flu diagnosed in a 25-year-old Mexican who flew to the city via Shanghai.

The Health Ministry said in a statement on its Web site that Bao left St. Louis, Mo., Thursday, transited St. Paul, Minn., on a flight that went to Tokyo.

In Tokyo he took a Northwest Airlines flight to Beijing on Saturday and then got on a different plane to Chengdu, the capital of southwestern Sichuan province, the ministry said.

On the last flight, Bao started experiencing symptoms that included a fever, sore throat, cough and a runny nose, the statement said.

Bao immediately sought treatment at the Sichuan People's Hospital and was diagnosed as a suspected case of Type A H1N1 influenza based on his symptoms and laboratory tests, the statement said.

Bao was transferred to the Chengdu Infectious Disease Hospital and people who came into close contact with the man during his medical examination have also been put under medical surveillance, the ministry said.

The ministry said it has asked local authorities to locate anyone who was in close contact with Bao and urged other passengers of the last two flights Bao was on to contact health authorities as soon as possible.

China has been accused in the past of not acting quickly enough to combat the spread of diseases, especially the 2003 global outbreak of SARS. Chastened by that experience and subsequent threats from avian flu, the government this time has acted quickly and decisively to block an outbreak, but some of its measures have been criticized as excessive.

The swine flu-prevention measures include bans on imports of pork from Mexico, some U.S. states and Alberta in Canada. Beijing has also canceled the only direct flights between China and Mexico, a twice-weekly service by Aeromexico. Authorities require arriving travelers with flu-like symptoms to report themselves and have placed some travelers under weeklong quarantines.

China's tough measures have drawn complaints from Mexico, the country hardest hit by the virus, that their citizens were being quarantined based merely on their nationality. China has defended the steps as necessary to block swine flu from entering the world's most populous nation.

The virus has killed at least 53 people and sickened more than 4,370 in 29 countries, mostly in the U.S. and Mexico, but has so far largely spared Asia.