Authorities and residents in southwestern Hokkaido continued to brace themselves Thursday for a major eruption of Mount Usu.
Seismic activity intensified through the day and volcanologists said the 732-meter volcano could erupt in the next few days.
In its second emergency bulletin issued at 1:20 p.m., the Muroran Meteorological Observatory southeast of Mount Usu said it has confirmed gaps and cracks over a length of more than 100 meters on the northwest side of Mount Usu.
"Crustal movements resulting from the expansion of magma under the ground have affected the surface of the earth. We need continued caution over a possible eruption," the Meteorological Agency said of the gaps, observed from a Self-Defense Force helicopter.