Another 10 people on a cruise ship quarantined in Yokohama have tested positive for a new coronavirus originating in China's Wuhan, the health ministry said Thursday, bringing the number of infected passengers on the vessel to 20.

The Diamond Princess, carrying around 3,700 passengers and crew from 56 countries and regions aboard, has been kept in quarantine at anchor off a pier in the Kanagawa Prefecture capital, south of Tokyo, after an 80-year-old passenger who disembarked in Hong Kong was found to be infected with the virus.

The 10 newly diagnosed passengers, in their 50s to 70s, were hospitalized. Four are Japanese, two American, two Canadian, one a New Zealander and the other from Taiwan. None came into close contact with the originally infected man from Hong Kong.

With virus test results on some 170 people pending, the cruise ship docked at Yokohama Port on Thursday to replenish food and other supplies such as masks, thermometers and medicine. The Defense Ministry plans to send up to 80 Self-Defense Forces personnel in addition to medical officers to the ship.

Japan remains vigilant against the spread of the pneumonia-causing virus with confirmed cases in the country standing at 45.

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Prime Minister Shinzo Abe said Japan will take an additional precautionary measure from Friday, denying entry to foreigners on a different cruise ship that has left Hong Kong, bound for Japan.

The decision came amid concerns about new coronavirus infections aboard the Westerdam, which a Japanese land ministry official says was on the way to its final destination, Yokohama port, provided no changes have been made to the original itinerary.

"We will adopt the same step (to ban entry to foreign nationals) if similar cases emerge," Abe said at a meeting of a government task force on the virus.

Japan has been stepping up its efforts to block the virus from entering its shores. Even without symptoms, foreign nationals who have been in Hubei Province, where Wuhan is located, two weeks prior to their arrival, and holders of Chinese passports issued in the province, are barred from entering the country.

The government is also seeking to evacuate Japanese citizens in the central Chinese province who wish to return home.

A fourth chartered aircraft to bring home about 200 Japanese nationals and family members left Tokyo on Thursday night, adding to the 565 Japanese that have already been repatriated on previous flights. The plane, a Boeing 767, is scheduled to return to Tokyo on Friday morning, according to the Foreign Ministry.

A Japanese government official said China is likely to allow Chinese spouses to board the plane to Japan with their partners.

The Chinese authorities have generally prohibited citizens from leaving Wuhan amid the virus outbreak, but Tokyo asked Beijing to allow Chinese spouses to accompany their Japanese partners "from a humanitarian standpoint," according to Chief Cabinet Secretary Yoshihide Suga.

Japanese authorities have taken samples from 120 people aboard the Diamond Princess, who have shown symptoms such as coughing and fever, as well as 153 others who were in close contact with them. To date, 82 of the 102 test results have come back negative.

The number of people infected with the virus on the Chinese mainland has topped 28,000, with the death toll reaching 563, according to the country's health authorities.

The epidemic has hit the Japanese tourism industry reliant on foreign travelers, particularly from China, sent consumers buying masks, and raised concern about the world's third-largest economy. Abe has stressed that the Tokyo Olympics and Paralympics will be held as planned this summer.

On the Diamond Princess, all passengers who are expected to remain isolated through Feb. 19, have been asked to wear masks, stay in their cabins and maintain a distance of about 2 meters from others when eating.

Despite the fresh discovery of people infected with the virus aboard the ship, the health ministry said the two-week quarantine period will remain the same as measures have already been implemented to prevent the infection spreading.

The elderly Hong Kong man flew to Tokyo in mid-January and boarded the cruise ship in Yokohama on Jan. 20. He disembarked in Hong Kong on Jan. 25.

After departing Yokohama on Jan. 20, the Diamond Princess stopped at Kagoshima two days later before arriving in Hong Kong. It then traveled to Vietnam and Taiwan before calling at Naha, Okinawa Prefecture, on Saturday and then returned to Yokohama on Monday night, according to its operator.

The ship passed quarantine in Naha but the ministry decided to repeat it following the discovery that the Hong Kong man had been infected with the coronavirus.

A medical expert said the number of infected people on the ship could grow as the new virus is believed to be just as contagious as the common cold or influenza.

"There is a possibility that those without symptoms have been infected, but the virus cannot be detected unless it propagates inside a body and is excreted," said Hiroki Takakuwa, professor at Kyoto Sangyo University.

He added it is pointless to test all aboard as there is an incubation period in which symptoms are not present.

While there is no drug to treat the coronavirus infection, starting symptomatic treatment early tends to lead to a faster recovery, according to medical experts.