TOKYO — For months, Japan has confounded the world by reporting a relatively low rate of coronavirus infections without imposing the kind of stringent measures used by other nations.

As the country now declares a state of emergency in the face of a worrisome rise in cases, medical experts are wondering whether the move on Tuesday has come just in time to avoid calamity, or is too little, too late.

Prime Minister Shinzo Abe, in announcing that the declaration would apply to Japan’s biggest population centers for the next month, painted an optimistic picture. By asking citizens to significantly reduce human-to-human contact, he said, “the expansion of infections can be turned to a decline in two weeks.”

But some experts said the state of emergency amounted to a tacit admission that the approach the country had stood by for months was no longer working, as Japan reached 3,906 confirmed cases on Tuesday, exactly double the number a week earlier.