TOKYO -- The U.S. says Americans aboard a quarantined cruise ship will be flown back home on a chartered flight Sunday, but that they will face another two-week quarantine.

About 380 Americans are aboard the Diamond Princess cruise ship, which has docked at Yokohama, a port city southwest of Tokyo. So far, 285 people from the ship have tested positive for the new virus that began in China, after 67 new cases were found Saturday.

The passengers have been quarantined on the ship since Feb. 5. That 14-day quarantine is due to end Wednesday.

A chartered aircraft will arrive in Japan late Sunday and American passengers will be flown to Travis Air Force Base in California, with some continuing to Lackland Air Force Base in Texas, the U.S. Embassy in Tokyo said in a letter to passengers and crew that was posted online Saturday.

Everyone will get a checkup before being allowed on the chartered flight, and those who show symptoms of sickness will not be permitted to board the plane, the embassy said.

After arriving in the U.S., all of the passengers will need to go through another 14 days of quarantine, the letter said -- meaning they will have been under quarantine for a total of nearly four weeks.

"We recognize this has been a stressful experience and we remain dedicated to providing all the support we can and seeing you safely and expeditiously reunited with family and friends in the United States," it said.

The U.S. State Department urged American passengers to return home.

"To fulfil our government's responsibilities to U.S. citizens under our rules and practices, as well as to reduce the burden on the Japanese healthcare system, the U.S. government recommends, out of an abundance of caution, that U.S. citizens disembark and return to the United States for further monitoring," the department said in a statement.

One of the American passengers, Matthew Smith, who has been tweeting aboard the ship, including photos of the food passengers have been given, expressed disappointment at what he called "a monkey wrench" the American government was throwing into the quarantine aboard the ship.

Smith complained about having to begin a new 14-day quarantine even though he was due to get off the ship next week.

"OK, so here's the thing: As long as the official plan by Japanese health officials is to release those of us who are still healthy from quarantine in just under four days, why would I want to interfere with that by taking up an offer from U.S. officials to fly us back to Travis?" he said on Twitter.

American passengers won't be the only ones facing a second quarantine, however. Hong Kong's government announced Saturday that it was arranging to bring back residents aboard the ship as soon as possible on a chartered flight, and that they will need to stay at a quarantine centre for two weeks upon arrival.

The letter to Americans on the Diamond Princess warns, "Should you choose not to return on this charter flight, you will be unable to return to the United States for a period of time."

Japan's Health Ministry allowed 11 passengers to disembark Friday, saying that those over 80 years old or with underlying medical conditions, as well as those staying in windowless cabins during the 14-day quarantine, can stay at a designated facility on shore.

Separately, the Japanese government said Saturday that a chartered flight to bring Japanese out of Wuhan -- the Chinese city at the centre of the outbreak of the virus -- will leave Sunday and return Monday. That would be the fifth such plane for Japan.

Besides the cases on the cruise ship, Japan has reported 55 others. Three new cases were reported Saturday in Wakayama prefecture in central Japan, and eight were reported in Tokyo.

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Associated Press writer Mari Yamaguchi contributed to this report.