Mount Asama, an active 90 miles (140kms) from central Tokyo has erupted, spewing ash over the greater Tokyo area.
Smoke from the volcano is reported to have shot up as high as 1 mile from the crater as it erupted at 1:51 a.m local time.
The volcano last erupted in August last year.
Residents nearby the volcano are on high alert but haven’t yet be evacuated, and an exclusion zone is in place closer in.
An eruption from Mount Asama killed 1500 people in 1783.