Fear of possible coronavirus infections on a cruise ship carrying about 3,700 people became reality Wednesday as 10 of 31 passengers tested were confirmed to have positive results, fueling unease among officials that the number could go much higher.

The outcome was based on the results available after 273 people aboard the vessel were examined, health minister Katsunobu Kato said Wednesday morning. The 10 disembarked the Diamond Princess, which is docked at Yokohama port, and were taken to four hospitals in Kanagawa Prefecture.

The development suggests more passengers and crew members on the cruise ship could be infected and may not know it — at least four asymptomatic cases have been reported in Japan. Remaining passengers and crew will be confined to the ship for at least two weeks, Kato confirmed.

The operator of the ship, Princess Cruises, revealed in a statement that the 10 are three Japanese passengers, two Australian passengers, three passengers from Hong Kong, one passenger from the United States and one Filipino crew member.

Their ages range from 50 to 80, according to the health ministry.

The operator said 3,711 people — 2,666 passengers and 1,045 crew members — were currently on board. Kyodo News said about half of the passengers were Japanese citizens.

The health ministry said it had checked the health condition of all those aboard, and collected samples from individuals with symptoms as well as those who had close contact with those individuals.

“We are going to adopt carefully thought-out measures to prevent the virus from spreading,” Prime Minister Shinzo Abe said. “The passengers’ and crew members’ health checks are our highest priority.”

In response to a concern raised by a ruling coalition lawmaker that those aboard may have to wait on the ship much longer than 14 days if more people test positive, the prime minister said authorities were asking them to stay inside their rooms to limit the risk of contact with the virus.

A Japan Coast Guard patrol boat pulls up beside the Diamond Princess, a cruise ship anchored off Daikoku Pier in Yokohama, on Wednesday morning to transport people who tested positive for the new coronavirus to hospitals. | KYODO

Initially, passengers were told they would be allowed to leave the ship once they received negative results for the coronavirus test. But Chief Cabinet Secretary Yoshihide Suga said the decision was reversed when more of the tests than expected produced positive results.

The ship became a subject of medical scrutiny when it was revealed that a man who disembarked in Hong Kong on Jan. 25 was infected with the virus. The vessel returned to Yokohama on Monday evening to undergo a quarantine inspection.

The operator said it had provided internet and phone availability for its passengers, adding that the cruise ship plans to “go out to sea” to perform tasks such as producing fresh water before bringing abroad food and necessities. “Princess Cruises will continue to fully cooperate with and follow the instructions of global medical authorities and the Japanese government,” the statement said.

Meanwhile, Foreign Minister Toshimitsu Motegi said a fourth charter flight was scheduled to leave Japan on Thursday to pick up about 200 people who wish to come back to the country.

Tokyo is working with Beijing to ensure Chinese nationals with ties to Japanese citizens, such as spouses, will be allowed to travel on the flight, Motegi said.

A man carries a box that appears to contain samples from people aboard the Diamond Princess, a cruise ship anchored off Daikoku Pier in Yokohama, on Wednesday. | KYODO

All 565 people who returned to Tokyo from Wuhan, the outbreak’s epicenter, via three charter flights last week were Japanese citizens. An overwhelming majority of them who are not hospitalized are staying at lodgings the government has provided.

Suga briefed reporters Wednesday morning that all those who have already returned to Japan have undergone medical testing. If they test negative on the last day of the 10-day health monitoring period, they will be able to go home, the top government spokesperson said.

The health ministry disclosed criteria Tuesday for the discharge of coronavirus patients from medical facilities in the nation. Patients will be discharged from hospital once they clear medical tests taken 48 and 60 hours after symptoms cease.

Meanwhile, in China, the number of cases of the new coronavirus has surpassed 24,000 and the death toll stood at 490 as of Wednesday.

Staff writer Reiji Yoshida contributed to this report.

RELATED PHOTOS A Japan Coast Guard patrol boat is seen alongside the Diamond Princess, a cruise ship anchored off the coast of Yokohama, on Wednesday morning. | KYODO

A Japan Coast Guard patrol boat pulls up beside the Diamond Princess, a cruise ship anchored off Daikoku Pier in Yokohama, on Wednesday morning to transport people who tested positive for the new coronavirus to hospitals. | KYODO

A man carries a box that appears to contain samples from people aboard the Diamond Princess, a cruise ship anchored off Daikoku Pier in Yokohama, on Wednesday. | KYODO