According to Volcano Discovery, at 11.17am UTC, the Sakurajima volcano erupted after previous eruptions earlier in the year. Pictures on social media from live cameras near Tarumizu City show smoke and lava.
The Japanese Meteorological Agency (JMA) issued a level 5 volcano warning, meaning evacuation.
Residents of Kagoshima City have been told to leave the area, after previously being told to avoid “entering the danger zone”.
Most of the city of Kagoshima is across the bay from the volcano but several residential areas within about 1.9 miles of the crater may be ordered to evacuate depending on the situation, NHK said.
It later reported that 51 people in the vicinity were being evacuated.
Public television channel NHK reported no damage as of publication, but added volcanic stones could be seen raining down up to 1.5 miles away from the site.
Fumio Kishida, the Japanese Prime Minister, has instructed the Government to take steps to protect lives.
Volcano Discovery also reported Sakurajima erupted on Saturday and Friday, as well as throughout July.
Sakurajima volcano in southern Kyushu is one of the most active volcanoes in the world, and one of the few which is at present in constant activity.
Sakurajima’s ongoing typical activity range from strong strombolian to large ash explosions every four to 24 hours.
The volcano is the historically active centre of the larger complex of the Aira caldera volcano.
Located across Kagoshima Bay, which separates the city and the volcano by 4.2 km of water, its summit is only 8 km east of the city of Kagoshima with a population of half a million.
Due to its explosive potential, it is considered a very dangerous volcano and is closely monitored.
The largest historical eruptions of Sakurajima took place during 1471-76 and in 1914.
Unlike the ash produced by burning wood and other organic materials, volcanic ash can be dangerous.
Its particles are very hard and usually have jagged edges and, as a result, it can cause eye, nose, and lung irritation, as well as breathing problems.
While in the air, ash can cause problems for jet engines, forcing airlines to cancel flights through the affected area.
An ashfall that leaves a thick layer of ash may cause roofs to collapse, clog gutters, and interfere with air conditioning units.
Animals in an area coated by volcanic ash may have difficulty finding food, as the plants in the region may be covered in ash.
Ash can also contaminate water supplies.