The declaration was the second, the first being in late February, made after seeing the pace of the novel coronavirus disease (COVID-19) infection is catching up.
The Japanese authorities only fear that the surge of infection cases without a certain source of infection could lead to a bigger, worse new wave of COVID-19 in the nation.
The request came a day after a government panel of medical experts said that Japan should not be relaxing even though being able to stem a surge in domestic infections.