Japan said it would temporarily tighten visa control for citizens of Mexico, the center of the swine flu outbreak.

Under the tightened rules, Mexicans could no longer obtain a visa on arrival, according to a Japanese foreign ministry official.

Japan has visa-waiver agreements with more than 60 countries and territories, including Mexico, allowing its nationals to obtain visas on arrival without application in advance.

Japan also plans to issue an advisory asking its nationals to postpone trips to Mexico following the swine flu, Foreign Minister Hirofumi Nakasone said Tuesday.

Japan said it will do its best effort to block the outbreak of the swine flu at the border to protect its people's safety.

Japanese health minister Yoichi Masuzoe said in a statement Tuesday his ministry has declared the outbreak of the new influenza following the World Health Organization's upgrading of its alert level.

The government will conduct quarantine activities on flights from Canada and the United States at three of Japan's key international airports as well as on flights from Mexico, having quarantine officers check passengers in the cabin before disembarking the aircraft.

Should people be suspected of infection with swine flu in Japan, the government will isolate them at designated medical facilities to prevent the disease from spreading.

The health minister also urged people to take care of themselves and avoid becoming infected with the new flu by gargling, wearing masks, washing their hands, and staying away from crowded areas as much as possible.

A task force headed by Prime Minister Taro Aso to deal with the situation has been set up. Counseling counters at local health centers have also been established across Japan.

The World Health Organization said Monday it has raised its alert level for a global flu pandemic to 4 from the current 3 due to the growing number of confirmed or suspected cases of swine flu in humans.

In Mexico alone, more than 140 people were killed by the pandemic.

Besides Mexico, the United States, Canada, Britain and Spain also reported confirmed swine flu cases, while suspected cases have been reported in other countries including New Zealand, Italy, France, Germany, Switzerland, Peru and most recently, South Korea.