The Japanese government is stepping up its protective measures, with a proposed pause on large public gatherings.
Prime Minister Shinzo Abe has suggested that major sport, cultural and other events should be cancelled, delayed or scaled down for about two weeks.
Abe said, "Now is the crucial time to contain the spread of the virus at an early date."
He added the government will ban foreign nationals from southern areas of South Korea from entering Japan starting Thursday.
The government has also set up a team of experts to tackle virus clusters a growing global concern.
Health Minister Katsunobu Kato said, "A cluster is a group of people infected with the virus in a chain. Clusters may produce other clusters. The government and experts are afraid of this kind of expansion."
The ministry says clusters may have already occurred in some parts of Japan, including Tokyo and the western prefecture of Wakayama.
In Japan, more than 860 people have been confirmed to be infected. Nearly 700 of them are from a quarantined cruise ship docked near Tokyo.
Health officials say an elderly person with the virus has died in the northern prefecture of Hokkaido, the second fatality outside the ship.
Four people from the vessel have died.