CNN  — 

Flights have been canceled across southern Japan after the country’s largest active volcano erupted, spewing thick clouds of ash high into the atmosphere.

Mount Aso rumbled to life on Monday morning, according to the Japan Meteorological Agency, causing disruption to air traffic serving Kumamoto Airport, 880 kilometers (550 miles) southwest of Tokyo.

Black smoke was sent as high as two kilometers, prompting the cancellation of at least 20 flights on Monday, according to NHK, Japan’s national public news network.

At least four more out-going flights from Kumamoto Airport, scheduled for early Tuesday have also been canceled.

ANA grounded at least two flights connecting Kumamoto, which is 20 kilometers from the volcano, to Osaka and Tokyo.

The airport serves mainly domestic routes, but has connections to Taiwan.

JAL announced on its website that “flights from and to Kumamoto airport are experiencing irregular operations.”

“We found that the smoke rose not only vertically but also horizontally. The eruption could have pyroclastic flows,” Sadayuki Kitagawa from the country’s meteorological agency says, referring to the fast currents of gas and hot rocks often emitted by active volcanoes.

Officials closed a four-kilometer-wide area around the crater and evacuated about 30 people.

The agency also issued a level three warning on its five-level scale, advising travelers to stay away from the volcano.

Mount Aso measures 128 kilometers in circumference and is 1,506 meters high.