The Nikkei reports on the matter
Citing a senior LDP official, the report says that Japan is expected to declare a state of emergency at 'any day' now in response to the virus outbreak in the country, but restrictions on individuals will not be compulsory due to the constitution.
The official also adds that Japan has not been using its full capacity to test up to 9,000 persons a day because Japanese law requires anyone found to be positive to be hospitalised i.e. they are not testing because of limited medical capacity to cope.
The full report can be found here.
