Crew members began leaving the coronavirus-stricken Diamond Princess cruise ship after weeks of quarantine on Thursday.

Japanese officials admitted that the quarantine "may not have been perfect" and said they could not isolate workers properly because they needed to run the cruise ship.

"We suspected some of the cruise staff may have already been infected," one official said.

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Crew members have finally begun to leave the coronavirus-stricken Diamond Princess cruise ship, after a weeks-long quarantine that many experts called unethical and ineffective.

About 240 workers who tested negative for the virus began to disembark on Thursday, Japan's Ministry of Health reported. All passengers have evacuated, but hundreds of workers remain — the ministry said it will take several days to get everyone off the ship. The crew will be transported to the National Tax College in Wako, outside of Tokyo, for 14 days of isolation.

Experts have harshly criticized the cruise-ship quarantine, saying that it might have helped the virus spread. As of Thursday, 705 people who were on the ship have tested positive, at least 150 of whom are crew members, CNN reported.

"We suspected some of the cruise staff may have already been infected, but ... they had to operate the cruise ship itself, they had to see the passengers, they had to deliver the meals," Dr. Norio Ohmagari, director of Japan's Disease Control and Prevention Center, told CNN. "So that may have caused some close contact with the cruise ship workers and also the passengers."

Ohmagari said that keeping the crew on board despite the risk of infection had been a "tough decision."

Another advisor to the Japanese government, Dr. Shigeru Omi, said at a press conference on Monday that officials were "very grateful" to the crew members.

"Obviously crew members were quite at risk," Omi said. "On human rights, of course we sympathize, but you know as far as the passengers are still there, they have to provide the service."

'We all are really scared and tense'

Crew members aboard the Diamond Princess cruise ship at the Daikoku Pier Cruise Terminal in Yokohama port, February 24, 2020. Kazuhiro Nogi/AFP/Getty

As the case count on the ship rose, some Indian crew members begged their government to rescue them, sharing a series of videos on Facebook. One of them, Binay Kumar Sarkar, told Business Insider that the situation on the ship was "out of control."

"There are lot of people who don't have coronavirus, so why are we all being confined here?" he said. "Please save at least those of us who are healthy."

Public-health experts seemed to agree.

"The quarantine was not justified, and violated the individual rights of the passengers while allowing the virus to literally pick them off one-by-one," Dr. Amesh Adalja with the Johns Hopkins Center for Health Security previously told Business Insider.

He added, "the whole idea of the cruise ship quarantine was ill-conceived, and the resultant slew of infections it spawned was completely predictable."

For crew members, conditions were even worse.

One infectious-diseases expert, Kentaro Iwata, said poor hygiene practices on the ship made him "so scared" of contracting the virus when he visited.

"The cruise ship was completely inadequate in terms of the infection control," Iwata said in a video on YouTube. "There was no distinction between the green zone, which is free of infection, and the red zone, which is potentially contaminated by the virus."

Though passengers were confined to their rooms, workers continued to eat together in the ship's mess hall. According to a New York Times report, infected crew members ate in the mess hall alongside their coworkers.

"We all are really scared and tense," Sonali Thakkar, a worker on the ship, told CNN.

"There are many places where we all are together, not separated from each other," she added. "Especially when we sit in the same mess hall and eat together, the place where it can spread very fast."

Crew members work on board the Diamond Princess cruise ship as the ship arrives at Daikoku Pier on February 12, 2020 in Yokohama, Japan. Tomohiro Ohsumi/Getty Images

Ohmagari admitted that the quarantine "may not have been perfect" and that "scientifically speaking," crew members should have been isolated just like passengers.

But workers could not be completely isolated, Yosuke Kita, a senior coordinator at Japan's Ministry of Health, said in the Monday press conference.

"Unfortunately to maintain daily life of the more than 3,700 passenger cruise, we needed help, we needed support from cruise members to maintain the daily life," Kita said.

Omi added that the majority of people who got sick likely got infected during their two-week cruise, before the quarantine started.

"I admit, our isolation policy was not perfect," he said. "No place is perfect except in a hospital."

Hilary Brueck contributed reporting.

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