The volcano, located in the far southwestern part of Japan's mainland on the island of Kyushu, began to erupt at 4:31 p.m. local time Sunday (3:31 a.m. EDT U.S. time).
Visibility in the city of Kagoshima, where the volcano sits, deteriorated quickly as ash spread into populated portions of the city of 600,000 residents, according to the English-language NHK World website.
Some passers-by shielded themselves from the ash with umbrellas. In addition, many drivers were forced to turn their car lights on in the darkened driving conditions.
The eruption is the latest in a string of recent natural calamities in Japan. A deadly, record-shattering heat wave has gripped Japan most of this month. Northern Japan suffered deadly landslides earlier this month and has seen additional heavy rainfall and floods in more recent days.