Japan's Mount Aso eruption spews giant column of ash

Japan's Mount Aso erupted yesterday, spewing a giant column of ash thousands of meters into the sky as hikers rushed away from the popular tourist spot.

No injuries were immediately reported after the late-morning eruption in southwest Japan, which sent rocks flying in a dramatic blast captured by nearby CCTV cameras.

People were warned not to approach the volcano as it ejected hot gas and ash as high as 3,500 meters, and sent stones tumbling down its grassy slopes.

Authorities said they were checking if any hikers had been trapped or injured, as TV footage showed dozens of vehicles and tour buses parked at a nearby museum that has a clear view of the volcano.

Pale grey torrents of ash were seen rushing down Aso's slopes towards the museum, but did not reach the site.

"Human lives are our priority and we are working with the Self Defence Forces, police and firefighters to effectively deal with the situation," Chief Cabinet Secretary Hirokazu Matsuno said in a televised news conference.

For those near the mountain, "caution must be exercised for large flying rocks and flows of pyroclastic materials," said Japan Meteorological Agency official Tomoaki Ozaki.

"Caution is warranted even in far-away areas downwind, as the wind may carry not just ash but also pebbles," Ozaki told reporters.

Ozaki also warned that toxic gases may also have been emitted.

The last time the JMA raised its warning for Aso to yesterday's level – three out of five – was when it erupted in 2016.