Mount Fuji has become visible more often from Tokyo than half a century ago, suggesting the air around the Japanese capital has become cleaner, a survey says.

In long-term observations from two schools in western Tokyo, the 12,388-foot volcano was visible on 126 days in 2012, nearly six times as often than in 1965, the Jiji news agency reported Friday.

Staff at the Seikei junior high and high schools have been checking whether Mount Fuji is visible to the naked eye at 9 a.m. each day from the roof of an 80-foot school building nearly 50 miles from the iconic volcano, long considered the symbol of Japan.

About 50 teachers and assistants have been involved in the project since it was initiated in 1963.

"I've never imagined that such a drastic change (in visibility) would occur," said teacher Atsushi Miyashita, 53, who joined the climate observation staff in 1990.

Severe air pollution around Tokyo that peaked in the 1970s has been reduced markedly thanks to tightened emission controls.