An eruption, measuring three on a scale of zero to five, was observed at 7:44 pm (1044 GMT) from the 2,568-meter (8,474-foot) high Mount Asama, the agency said.

The agency said tremors related to the mid-scale eruption continued, urging local residents to monitor volcano activity on the mountain which lies some 150 kilometers (95 miles) northwest of Tokyo.

But local authorities did not issue an evacuation warning and there were no reports of injuries.

"We observed some sticky rain containing volcanic ashes but there was no real damage from the latest eruption," a local police official said.

Mount Asama last went up on September 1, the volcano's most violent activity since April 1983. The eruption threw rocks over a wide area and caused a forest fire.

Prior to this month, Mt Asama last erupted in April last year.