YOKOHAMA, JAPAN (NYTIMES) - As coronavirus cases rapidly multiply on a quarantined cruise ship, the more than 2,500 passengers on board live in effective isolation.

They receive meals in their cabins. They keep an officially mandated distance of 1.8m from one another for the few minutes each day that they are allowed on deck for walks.

Below decks, the situation is different. There, hundreds of crew members are eating, living and working elbow to elbow as they try to keep life as comfortable as possible for those above. They line up for simple buffet meals and then sit down together to eat. Bathrooms are shared by up to four people, and cabins often by two.

These conditions have raised fears that a quarantine meant to halt the virus' spread on board, and keep the contagion from expanding on Japan's shores, is endangering the health and safety of the crew.

The ship, which is under a two-week quarantine in the port of Yokohama, has become host to the highest concentration of coronavirus cases outside China, the epicentre of the outbreak.

The risk to crew members and passengers was dramatically reinforced on Monday (Feb 10) when Japan's health ministry said that an additional 65 people had tested positive for the virus, nearly doubling the total to 135.

Among them, at least 10 crew members have been infected, with five cases announced on Sunday and five more Monday. According to employees, the infected crew members identified on Sunday had been eating in the mess hall alongside their co-workers.

Unlike the passengers they serve, most of whom come from wealthy nations, the ship's employees are overwhelmingly from developing countries like India and the Philippines. They have not received the same global attention as passengers from countries like the United States, Australia and Britain, whose social media posts have been widely read.

In a video posted to Facebook on Monday, Mr Binay Kumar Sarkar, who works in the ship's galley preparing meals and washing dishes, asked the Indian government to help get him and his co-workers off the ship before the virus spread further. There are 132 Indians among the crew of more than 1,000.

The ship is like a "small city", Mr Sarkar said in a Facebook chat, making it "very easy" to spread the virus.

In response to e-mailed questions, a representative of Princess Cruises, which operates the Diamond Princess, said that all crew members "are highly trained in safety and public health standards".

Without offering specifics, the representative added that the company was "implementing processes developed in coordination with public health officials to support the elevated requirements of this situation".

In some ways, the cruise ship quarantine is analogous, albeit with a much smaller pool of people, to the lockdown of Wuhan, China, where the epidemic began. In Wuhan and the surrounding province, Hubei, the authorities have barred close to 50 million people from leaving, and cases there are still rising as family members infect one another.

"Similar to the situation in Wuhan, but at a smaller scale, by quarantining the ship, the crew members are being forced to stay together, which increases the likelihood of transmission," said Dr John B. Lynch, an associate professor of infectious diseases at the University of Washington. "We have to remember that quarantines protect those outside the quarantine, not those within."

Other experts said supervisors on the ship needed to enforce strict hygiene policies, including frequent hand-washing. Both passengers and crew members should also be "keeping distance from others and avoiding congregating", said Dr Peter Rabinowitz, who is co-director of the University of Washington MetaCenter for Pandemic Preparedness and Global Health Security.

Crew members, who spoke on the condition of anonymity for fear of losing their jobs, said they had been provided with masks, gloves and hand sanitiser, but given little training on how to reduce their chances of infection in a situation of this magnitude.

Like passengers, they have been given thermometers and told to monitor their own temperatures and report back if they develop a fever. They have received no new guidance since the quarantine began a week ago, according to one employee.

Passengers said they were grateful to the crew but also worried that the employees, even though they are wearing protective gear when they enter cabins, might be passing the infection to people isolated inside.

On Monday, passengers were given new masks designed to filter out 95 per cent of airborne particles, as well as packages of alcohol wipes. The Centres for Disease Control and Prevention in Atlanta, United States, also sent a letter to passengers advising them to wear face masks if they shared cabins with other passengers and to avoid sharing personal household items.

Japan's health ministry said on Monday that so far it had tested 439 people on the ship for the coronavirus. That leaves more than 3,000 who have not been tested, receiving only initial health checks.

Japanese officials have said they do not have the capacity to test everyone on the ship. But on Sunday, Health Minister Katsunobu Kato said his ministry needed to consider whether it could do so.

In Hong Kong, where another cruise ship, the World Dream, has been held at port, about 1,800 crew members aboard were tested for the coronavirus after the authorities said that infected passengers had disembarked on Jan 24 in Guangzhou province, China.

When the ship arrived in Hong Kong last Wednesday on a subsequent journey, health authorities first tested those who had fevers or showed symptoms of the virus. All of those initial tests came back negative, but out of an abundance of caution, Hong Kong health authorities decided to test all crew members.

The Yokohama cruise ship terminal where the Diamond Princess is docked has been closed to the public. On Monday, a sort of war room had been set up where around a dozen people sat at computers and on phones.

Some of them wore jackets that identified them as members of a psychological support team. The room's walls were plastered with long strips of butcher paper, where information about the patients and a timeline had been scribbled in thick black marker.

At the port, the daughter of a passenger tried to deliver food and water to her elderly mother, who she said had a fever and was having trouble getting attention from the medical staff.

"She feels sick. I hope she can disembark soon," Ms Etsuko Takashima said through tears as she spoke about her mother, Madam Ayako Jinnai, 84. "At least, I hope she can get a drip infusion in the medical room on the ship. I don't think her current condition is known to the staff."