Japan's Meteorological Agency has raised the volcanic alert level for Mount Hakone, which is in a hot spring resort town outside Tokyo.
The agency boosted its alert level to two on a scale of five early Sunday. It is warning of the possibility of an eruption and large volcanic rocks falling around the crater in the Owakudani valley.
It's the first time in four years that the alert level for the volcano was set at two.
The agency made the decision after the number of volcanic earthquakes at Mount Hakone increased to 45 the day before. As of 9 a.m. on Sunday, 21 tremors have been observed.
The agency says small, shallow-focus quakes have been increasing in some areas near Mount Hakone since mid-March.
Officials of the town of Hakone have decided to restrict travel near the crater and have set up fences to block access.
A vendor near Owakudani said he's concerned because customers had just started to return after the eruption four years ago. He added that he is praying for the volcano to calm down and can only wait for it to do so.
The operator of Hakone Ropeway has suspended the service. A temporary bus service is running instead.
A man on a trip with his wife said he experienced shaking while eating. He said he is disappointed because he came to see the view of Mount Fuji from Owakudani.
A tourist from Australia said he was looking forward to taking the ropeway, but will try to find another way to enjoy nature in the area.