CAIRO — More than two dozen American tourists are being quarantined on a cruise ship in the Egyptian city of Luxor, according to two passengers, as the country's health officials declared 33 new cases of the novel coronavirus Saturday.

At least 26 Americans, all part of the same tour group, were in the middle of their once in-a-lifetime, 12-day dream vacation in Egypt. They had seen the pyramids and the Great Sphinx in Giza and had boarded a luxury ship, the Asara, for a Nile cruise.

That all ended when they arrived in the fabled city of Luxor on Friday. That’s when they learned that 12 Egyptian workers on their vessel had tested positive for the virus that causes covid-19 during a previous cruise. Then the American passengers were tested too. At least three Americans are suspected of testing positive for the virus, passengers on the ship said.

Instantly, they had joined the passengers of other luxury cruise ships around the world that have become floating quarantine zones, with the latest ship stranded off the coast of San Francisco. And like those passengers, the Americans aboard the Asara are in limbo, filled with uncertainty and fear.

“I’m terribly afraid that there’s no assurance we won’t get sick at some point,” said Amy Khamissian, 65, a paralegal from Miami.

On Saturday, Egypt’s health minister announced that 19 of the foreigners aboard tested positive, along with 14 more Egyptians believed to be crew members. Eleven of the Egyptians later tested negative after a second test, said Hala Zayed, the minister.

Before Saturday, Egypt had 15 confirmed cases of the virus, but many Egyptians are concerned the numbers are far greater. The government has a long history of obscuring information considered damaging to Egypt’s image and tourism-driven economy.

Khamissian and another Miami resident, Javier Parodi, 35, a building inspector, were told they tested negative on Saturday night, hours after they had been instructed to stay in their cabins. Their guide, they said, had told them that one American in their group had tested positive.

“Everything was normal, and now things are taking a turn to the not-so-normal,” Parodi said.

A spokesman for Egypt’s Health Ministry declined to comment on the presence of quarantined Americans or other foreign nationals on the ship. A U.S. Embassy official in Cairo did not respond to a request for comment. The embassy on Saturday tweeted a statement that read: “The Embassy has been informed that there are U.S. citizens on a Nile Cruise ship on which 12 crew members tested positive for the coronavirus. The Embassy is working to provide consular services and assistance, in coordination with the Egyptian government.”

On Thursday, Maryland’s governor said that three travelers from Montgomery County tested positive for the virus after returning to the United States from a trip on the same cruise. On Feb. 28, a Taiwanese American who had been on the same vessel tested positive once back in Taiwan.

As many as 28 tourists, from the United States, Greece, France and Canada, have tested positive for the virus after visiting Egypt in recent weeks. Some of them were on Nile cruises, but it’s unclear whether they were all related to the Asara.

The case of the Taiwanese American triggered the inspection of the crew of the Asara. She had traveled on the ship between late January and Feb. 1 and apparently passed on the virus to crew members, Egyptian Health Ministry and World Health Organization officials said.

It now appears likely that the infected crew, or at least some members, continued working on the vessel in February, until the WHO told Egyptian authorities March 1 that the Taiwanese American woman had tested positive.

When the Asara arrived in Luxor on Friday, the group’s travel company, Gate 1, sent the American passengers a letter. It said that U.S. Centers for Disease Control and Prevention personnel had informed the company of “possible exposure” to the coronavirus on the Asara during a cruise Feb. 12 to Feb. 19. The CDC asked for names and contacts of Gate 1 passengers aboard the ship, according to the letter, which was obtained by The Washington Post.

Their tour guide said there was one case of a passenger who was quarantined two weeks ago when he arrived in Oslo, according to Khamissian and Parodi.

The letter said they could get off the ship if they wanted to or continue their vacation. They weren’t told there were 12 workers infected onboard.

On Saturday night, infected passengers were taken off the ship to go into isolation on land. At least three Americans were placed on a military plane and flown to the city of Marsa Matruh for observation at a hospital that has so far treated Egypt’s cases, said one of those hospitalized, Matt Swider, a technology journalist from New York.

“I am feeling fine,” he said in a phone interview before boarding the plane. “Others around me seem mildly ill.”

“My Twitter and Facebook are filled with wonderful photos, which ends now sadly,” he added.

The Americans who tested negative were told to remain on the ship for another 14 days.

Khamissian and Parodi had planned to get off in three days.

Before they left for Cairo on March 1, they heard about the cases of foreigners testing positive for the virus after visiting Egypt. That didn’t stop them from their vacation. Khamissian and Parodi packed extra soap, hand sanitizer and wipes. They disinfected surfaces and seats. “It felt like we were doing everything right,” Khamissian said.

Then they started reading headlines about the ship they were on and reached out to the U.S. Embassy in Cairo for help. “You don’t want to be the boat you’re reading about in the New York Times and Washington Post,” Parodi said.

They said they want the U.S. government to intervene because they don’t feel fully informed. They were told before they received their results that they would be allowed off the ship, but now the quarantine is being enforced, Khamissian and Parodi said.

“We are kind of in limbo and in the hands of the Egyptian government, and we would rather be in the hands of the American government,” Khamissian said.

They worry about being stuck on a ship that size, which is smaller than the Diamond Princess that was also quarantined for 14 days in Japan. “We’re walking on eggshells,” Khamissian said, “and I’m scared.”

Kornfield reported from Washington. Heba Farouk Mahfouz in Cairo contributed to this report.