Satellite images of Nishinoshima acquired on 19 April and processed by NASA's Earth Observatory showed an area of hot lava in the crater.
According to a news article, observers aboard a plane passing the volcano on 21 April noted intense activity in the crater.
Bombs were ejected as high as 100 m above the crater and incandescent rocks rolled down the flanks, reaching the sea.
The report noted brown plumes rising from the crater and lava effusing from an area near the top of the vent.
Sources: Asahi,NASA Earth Observatory