A small-scale eruption hit Mount Aso in Kumamoto Prefecture on Monday, the first since Oct. 23, the Meteorological Agency said.

The eruption spewed smoke about 700 meters above the No. 1 crater of Mount Nakadake, one of the five peaks that constitute Mount Aso, the agency said. There were no reports of injuries.

The agency maintained the volcanic alert level at 2 on a scale of 5, warning people not to approach the crater as rock slides could occur om the area.

"An eruption of this level can happen at any time," said an official with the Meteorological Agency's Fukuoka Regional Headquarters.

The alert level for Mount Aso was raised to 3 — warning people against approaching the mountain — following an eruption Sept. 14. The level was lowered on Nov. 24 amid diminished volcanic activity.