As you may know in the news, Mt. Ontake, the 3067-meter volcano, erupted on Sep 27, Saturday.

I want to express my deep sorrow that around 30 climbers climbing on the top of the mountain seem to have died.

You cannot enter ONLY the 4km-radius cautionary zone from the summit of Mt. Ontake. Matsumoto is 60km from Mt. Ontake so does not affect the ordinal life and travel.
Tsumago, Magome, and Narai-juku of Nakasendo, which is a very popular walking course among foreigners, can be also travelled safely.

All trains, buses, roads in Nagano Prefecure except inside the cautionary zone are operating as usual.

The Kiso area and Mt. Ontake that has Ski Resort in the mountain foot are very nice places. I hope the eruption would calm down and missing climbers would be found soon.

See also this blog.

Mt. Ontake, the 4km-radius cautionary zone, and major sightseeing spots:

See a large map.