Japan's Meteorological Agency said visibility was down to less than 5 miles in several major cities, including Fukuoka, Kyoto, Osaka and Nagoya, Kyodo News Service reported. Problems were expected to persist through the weekend.
When visibility falls to 3 miles, it starts to interfere with transportation, experts said.
Some local governments released air quality warnings, saying residents -- especially those with respiratory diseases -- should wear masks while outdoors. Residents in Fukuoka were advised not to hang laundry on outside lines.