TOKYO, Jan. 30 (Xinhua) -- The Japan Meteorological Agency (JMA) on Tuesday raised its alert level for Mount Zao, a volcano which straddles Miyagi and Yamagata prefectures in northeastern Japan, stating that it had detected volcanic tremors and that an eruption was possible.

On the JMA's alert scale that peaks at five, the agency raised its warning from 1 to 2, advising people not to approach the volcano's crater.

According to the JMA, if an eruption were to occur, volcanic rocks could fall within a 1.2 km radius from the crater.

The agency said that in addition to tremors being detected at around 7 p.m. local time on Sunday and again at around 1 a.m. on Tuesday, more sizable crustal movements were recorded on Tuesday afternoon.

The slight crustal shift, a result of heated underground water and volcanic gas moving, was recorded at 2:18 p.m. local time and continued for 31 minutes, the JMA said.

Swelling of the southern slope of the mountain has also been observed from a monitoring point in the region and emitting volcanic gases are being monitored.

Along with the tremors, these phenomena indicate a possible increase in volcanic activity, the JMA said.

Prefectural officials in Yamagata have issued an evacuation advisory for the vicinity of the crater and a neighboring ski resort has been put on alert.

The eruption on Jan. 23 of craters near the peaks of Moto-Shirane on Mt. Kusatsu-Shirane in Gunma Prefecture, north of Tokyo, killed one person and left 11 others injured at a ski resort in the vicinity.