Wednesday's confirmation of further coronavirus infections aboard a quarantined cruise ship docked near Yokohama has put the city of Naha in Okinawa Prefecture, where the ship made a stop last Saturday, on high alert.

Tadashi Nakasone, an official from the Naha Municipal Government, said that staff members were verifying whether any passengers who left the Diamond Princess had spread the virus while it was docked in the city.

"We've received information that on Feb. 1, 13 passengers left the ship without returning after it docked in Naha and that those individuals have already left Okinawa Prefecture," Nakasone said Wednesday by telephone. He added that nearly all of the other passengers, numbering over 2,600, also came ashore temporarily to go sightseeing.