As you may have already heard, North-Eastern Japan has been affected by an earthquake and Tsunami at 11th March, 14:45 Japan Time.
Currently it appears the worst affected areas are the Northern coastal areas of Honshu. At the moment JR-East Rail services to the north have been affected by these events. Tokyo train services have also been suspended as a precaution. We will know more over the weekend, but journeys to the north of Japan will certainly be disrupted for the foreseeable future.
I've posted some useful telephone numbers below