The government began asking travelers from bird flu-affected areas Tuesday to have their shoes disinfected upon arrival at the country's four major international airports, including Narita, an official said.

The voluntary measure is aimed at preventing poultry droppings -- deemed a source of the bird flu infection -- from being brought into the country, Agriculture, Forestry and Fisheries Ministry spokesman Masanori Hayashi said Monday.

The H5N1 strain has killed at least 67 people in Asia, and authorities fear the disease could mutate into a form that can pass from human to human, sparking a pandemic.

Japan had its only confirmed human case of bird flu last year, but the patient recovered.

Hayashi said the measure is mainly aimed at people who have visited poultry farms or markets selling live birds in the 11 countries hit by the deadly H5N1 strain.

Travelers entering Japan from those countries will be asked to stop at quarantine centers at Narita airport, Central Japan International Airport in Aichi Prefecture, Kansai International Airport in Osaka Prefecture and Fukuoka Airport to have their shoes disinfected. The 11 countries are China, Cambodia, Indonesia, Thailand, Vietnam, Laos, Mongolia, Russia, Kazakhstan, Turkey and Romania.