The Ministry of Health, Labor and Welfare said it has tested 336 potentially infected people from around 3,700 passengers and crew on the vessel, and the latest results on 57 people turned up the six new cases.
The ship, carrying customers from more than 50 countries and regions, has been kept in quarantine since Monday after a passenger, who disembarked in Hong Kong, was found to be infected with the pneumonia-causing virus.
The government is also working on a request to get medication to those on board who are suffering from chronic conditions, health minister Katsunobu Kato said on a TV program the same day.
The overall number of infected in Japan now stands at 96, including 10 people who evacuated from the Chinese city of Wuhan, at the center of the outbreak, on government-chartered flights. Another 16 includes tourists and a tour bus driver.
The cases of confirmed infections have risen to more than 37,000 nationwide.