TOKYO -- A volcano in southern Japan blasted out chunks of magma Friday in the first such eruption in 22 years, causing flight cancellations and prompting warnings to stay away from its crater.

The Japan Meteorological Agency said that Mount Aso spewed out lava debris and smoke, shooting plumes of ash a kilometre into the sky. Dozens of flights from Kumamoto, the nearest city, were cancelled.

The observatory did not expect the eruption to increase in scale. Mount Aso, about 1,000 kilometres southwest of Tokyo on Kyushu island, is one of the world's largest. Earthquakes and other seismic activity stepped up in late August.

Eruptions by another volcano, Mount Ontake, in Nagano west of Tokyo killed more than 50 people in late September.