Cedar pollen, a major cause of hay fever, may be prevalent in Japan until mid-May, about a month longer than average, according to weather information provider Weathernews Inc.

"The pollen usually stops flying in mid-April, but this year it will continue flying in April in many areas and will be found even after the Golden Week holiday season until around mid-May in some areas, except for the Tohoku region," the company said in a press release.

The amount of pollen is expected to surge 10- or 20-fold over 2004 and twice as much as in an average year due to the hot summer last year, the company said.

Regions from Kanto to Kyushu are expected to see the first cedar pollen at the beginning or middle of February, it said.

The Sanin, Hokuriku and northern Koshin regions, and the southern Tohoku region on the Pacific side, will probably see pollen in mid- or late February, Weathernews said, while the rest of Tohoku will see the first instances in early or mid-March.

Weathernews defines the beginning of pollen activity as the time when more than one particle of pollen per square centimeter is recorded for two straight days.

"This year will likely see the largest or second-largest amount of cedar pollen ever," Seiken Sugiura, deputy chief Cabinet secretary, told a news conference after a meeting of Cabinet ministers.

Environment Minister Yuriko Koike separately said the cedar pollen count could have a serious social impact, given the likelihood of hay fever damaging efficiency at offices and factories.