Kumamoto Prefecture advised residents to stay indoors or wear masks if they go outside Tuesday in the nation’s first official health warning over heavy smog drifting in from China.
Kumamoto officials said the quality of air was likely to be substantially below national standards, amid warnings of health risks for the young and the sick.
Of specific concern is the concentration of PM2.5, or particulate matter 2.5 microns or less in diameter, which has been as high as 50 micrograms per cubic meter in several parts of Kyushu.
The government-set safety limit is 35 micrograms. The Environment Ministry last week said local authorities should issue warnings when concentrations rise to an average of 70 micrograms per hour.
The Kumamoto Prefectural Government said local readings were as high as 110 micrograms in some places Tuesday morning.
It advised local residents to stay indoors and not to exercise outside, while encouraging them to wear surgical masks if they ventured out.
A thick fog of pollution has blanketed Beijing and other Chinese cities a number of times over recent weeks.
Last month, Japanese media reported a swirl of pollution was making its way to Japan from China, further complicating already-strained relations between Tokyo and Beijing exacerbated by a territorial dispute.
Kyodo News reported Tuesday that the environment ministers of Japan, China and South Korea will meet in May to discuss ways to combat pollution.
The toxic haze that blankets China has been blamed on emissions from coal-fired power stations as well as exhaust fumes from vehicles on the traffic-clogged streets of the world’s largest auto market.
Scientists say prevailing winds are carrying airborne particles from the Asian mainland to Japan.
The phenomenon was first observed with the fine yellow sand from the deserts of Mongolia and China that accumulates on cars and buildings in Japan at certain times of the year.