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The confirmation set off a round of testing for 273 people who either showed symptoms or had close contact with the patient who disembarked in Hong Kong, Kato said.
Ten of the first 31 people tested were positive for the virus, he said. Samples from the 242 other passengers and crew are still being tested.
The 10 people showed signs of novel coronavirus, but none needed to be carried off the ship on stretchers, Kato said.
About 3,700 people are aboard the cruise ship — 2,666 guests and 1,045 crew — according to the cruise ship company. They will be held in protective quarantine for 10 to 14 days, Kato said at a news conference.
"Princess Cruises will continue to fully cooperate with and follow the instructions of global medical authorities and the Japanese government," the company said. It added that the ship would ensure that those who are quarantined have internet and phone access and would be made comfortable.
Princess Cruises said in a statement that two cruises that had been scheduled to leave Yokohama on Tuesday and Feb. 12 have been canceled.
By Tuesday, more than 20,000 novel coronavirus cases had been confirmed in mainland China, with 425 deaths, China's national health commission said. The illness was first detected in Wuhan, which is at the center of the outbreak.
There are 11 confirmed novel coronavirus cases in the U.S., according to the Centers for Disease Control and Prevention. Other people are being tested. The U.S. has suspended entry for foreign nationals who have visited China in the last 14 days, and it has announced other measures for people coming into the country from China.
Phil Helsel is a reporter for NBC News.
Arata Yamamoto has been a NBC News producer in Tokyo since 1993.