Halfway through a two-week quarantine, 65 more people aboard the Diamond Princess cruise ship in Yokohama have tested positive for the novel coronavirus, bringing the tally to 135 with only a fraction of the passengers tested, Princess Cruise Lines said Monday.

This means there are now more than 150 confirmed cases in Japan, if the 135 from the Diamond Princess are included.

The ship was put under quarantine soon after its return on Feb. 3 after a passenger who disembarked in Hong Kong was confirmed to have the pneumonia-causing virus.

The government is now preparing to test dozens of elderly passengers as it investigates potential issues with hygiene control on the infected ship.

But Chief Cabinet Secretary Yoshihide Suga indicated during a news conference Monday afternoon that it would be difficult to test all of the passengers and crew, adding that testing will be prioritized for people with potential symptoms and the elderly.

Earlier in the day, the Health, Labor and Welfare Ministry had said it was considering testing all of the now roughly 3,600 people aboard when the two-week quarantine ends on Feb. 19. Once their results are clear, they would be permitted to disembark.

No timeline was given for the process.

The ministry had said earlier that disembarkation might be possible on Feb. 19 but the passengers would have to wait for results.

“We need to properly address the unease and concerns of our citizens,” health minister Katsunobu Kato said.

Chief Cabinet Secretary Yoshihide Suga said Monday that it might be difficult to test everyone aboard the ship.

Only 336 passengers had been tested as of Monday, according to the health ministry.

The overall tally for confirmed cases includes 10 Japanese who were evacuated from the Chinese city of Wuhan, the center of the outbreak, on government-chartered flights, and 16 others, including tourists, tour guides and a bus driver.

The government has supplied requested medication to around 750 of the some 1,850 passengers who had made such requests as of Sunday and is working to supply the rest.

The Diamond Princess departed Yokohama on Jan. 20 and returned on Feb. 3 after visiting Kagoshima, Hong Kong, Vietnam, Taiwan and Okinawa. Passengers who were confirmed as infected upon arrival have been hospitalized in Japan.

U.S. company Princess Cruise Lines Ltd., which runs the Diamond Princess, said Monday that it will fully refund all passengers who were unable to disembark at Yokohama because of the outbreak.

The refund will include the cost of the cruise, hotel accommodations prior to and following the cruise, on-shore excursions and services used aboard the ship.

Passengers who were taken to medical facilities after testing positive for the virus or who were hospitalized for other reasons, will also be eligible.

The company will also cover all costs incurred by those quarantined since last Tuesday. The passengers were originally scheduled to disembark at Yokohama.

The cost of staterooms for the 16-day cruise ranged from ¥295,000 to ¥478,000, depending on type and inclusion of a balcony, according to the company. Suites ranged from ¥1.08 million to ¥1.38 million.

The Land, Infrastructure, Transport and Tourism Ministry said Monday that 13 of the 14 foreign cruise lines that were scheduled to dock in Japan this month have canceled their Japan stopovers.

The remaining cruise ship, the U.S.-operated Ocean Dream, is set to dock at Yokohama on Saturday and Kobe on Sunday.

The number of passengers aboard the Diamond Princess cruise ship who have tested positive for the novel coronavirus has been corrected to reflect a revision by the cruise operator.

RELATED PHOTOS A passenger looks out from a cabin balcony on the quarantined cruise ship Diamond Princess in Yokohama port on Sunday. | AP