The U.S. government is preparing to repatriate American citizens from aboard the Diamond Princess cruise ship, site of the biggest outbreak of the novel coronavirus outside China.

About 380 Americans and their families on the ship, docked in Yokohama, Japan, will be offered seats on State Department-organized planes flying back to the U.S. A State Department representative said aircraft to evacuate Americans would arrive in Japan on Sunday and that the U.S. government recommended that American citizens disembark and return...