The 2,568-meter-high (7,700-foot-high) mountain, some 150 kilometersmiles) northwest of Tokyo, puffed the smoke for two minutes early Monday, a spokesman for the agency said.

"The activity was very small and posed no threat to humans," the spokesman said.

The volcano in Nagano, the site of the 1998 Winter Olympics, last erupted in 1990 when it spat ash over a small area.

In 1947, 11 mountaineers died after being hit by volcanic cinders from an eruption on the mountain that year.

Mount Asama's last major eruption was in 1783, the agency said.

SPACE.WIRE