China has tightened visa rules for citizens from the United States, which has reported the second highest number of swine flu cases in the world.

According to a notice dated May 3 on the website of the Chinese Embassy and its consulates in the U.S. said that all visa applications would now require six business days to process, with express and rush services for visa applications suspended until further notice.

The new visa regulation, effective as of May 4, appears to apply to all Chinese visas, including tourist and business categories. Visa applicants are also required to fill out a form declaring which countries and U.S. states they had visited two weeks ago. Previously U.S. nationals could obtain visas in as little as one day.

More than 1,400 people globally have been infected with swine flu, with Mexico reporting the most confirmed cases with 802. The United States so far has reported 380 cases in more than 30 states.

On Tuesday, Chinese Foreign Ministry spokesman Ma Zhaoxu refused to address the specific visa changes for Americans, saying the changes is non-discriminatory and is not targeted at any country.

Since last weekend a Mexican traveler flying to Hong Kong via Shanghai was diagnosed with the illness, more than 70 Mexicans had been quarantined in hotels and hospitals in mainland China.

A plane chartered by the Mexican government arrived in several cities in China on Tuesday to pick up these and other Mexican citizens and take them home.

A group of 29 Canadian students and their professor were also being held in isolation in China. Two Americans were in isolation while another two who were in quarantine have been released.

Last year, China severely tightened visa regulations ahead of the Olympic Games in August as part of a wider security clampdown. And earlier this month, travel agencies in Hong Kong reported that visa restrictions were being tightened again ahead of the 60th anniversary in October of the country's founding.