The U.S. State Department on Saturday called for "increased caution" when traveling to Japan, escalating the alert to level 2 on the four-level advisory scale amid reports that a new coronavirus originating in China is spreading in Japanese communities via unknown infection routes.

The previous advisory at level 1 called on citizens to exercise "normal precautions" in Japan. As for China, the travel advisory has been raised to the highest level of 4, which urges citizens not to travel to the country.

According to the State Department, many infection cases of the pneumonia-causing virus have been associated with travel to or from mainland China, or being in close contact with such travelers.

But "sustained community spread" has been reported in Japan, which means that people in the country have been infected with the virus, though "how or where they became infected is not known, and the spread is ongoing."

Older adults and those with chronic medical conditions may be at higher risk for severe disease, the department said, advising such people to consult with a healthcare provider before traveling to Japan or consider postponing the trip if it is unnecessary.

So far, about 750 people have tested positive for the coronavirus in Japan, the highest number after mainland China where more than 70,000 people have been infected, resulting in over 2,300 deaths.

Most of the people infected with the virus in Japan are passengers or crew members of the quarantined Diamond Princess cruise ship docked in Yokohama, near Tokyo.

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