Four passengers have died aboard Holland America Line's MS Zaandam ship, according to leaked audio from a sister ship sent to rescue stranded passengers.

"Holland America Line can confirm that four older guests have passed away on Zaandam," a Holland America representative told Business Insider in a statement. Medical staffers and the representative have confirmed at least two cases of COVID-19 on board.

A crew member aboard the MS Rotterdam, which was dispatched to supply the Zaandam with COVID-19 testing kits and other medical supplies, sent Business Insider a memo breaking down a proposed rescue mission in which healthy Zaandam passengers would be transferred to the Rotterdam and sail toward San Diego.

Holland America has confirmed there are 138 sick passengers and crew members on board the Zaandam.

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Four passengers have died aboard Holland America Line's stranded MS Zaandam cruise ship, according to a recording leaked to Business Insider from a sister ship sent to rescue healthy passengers.

"I am also sad to share that four older Zaandam guests have passed away," the captain of the MS Rotterdam said in the recording of a shipwide announcement provided to Business Insider. "Three between yesterday and last night, and one a few days ago. Our thoughts and prayers are with their families, and the Zaandam team is doing everything they can to support them during this difficult time."

A Holland America crew member sent Business Insider a recording of the Rotterdam's captain announcing the deaths, as well as news from medical staffers confirming at least two cases of COVID-19 aboard the Zaandam.

The Rotterdam rendezvoused with the Zaandam on Thursday night off the coast of Ecuador to deliver medical supplies, including COVID-19 tests. The Rotterdam has no guests on board, but crew members on the ship have said it is staffed with 611 people.

According to a memo leaked by a Rotterdam crew member, the ship is now also tasked with rescuing healthy Zaandam guests.

The crew member sent Business Insider pictures of a printed memo dated Wednesday and titled "Rotterdam Humanitarian Mission FAQ." The rescue-response memo began with the question "Why do we need to do this?"

"This is a humanitarian action to help a sister ship which has an outbreak of respiratory illness mainly affecting your team mates, particularly food preparation and service staff," the memo said. "There is no other place for us to take the guests and no other means to provide assistance to the Zaandam and our fellow team members on board."

In a statement to Business Insider, a Holland America representative confirmed the course of action outlined in the memo.

"Today we announced a plan to transfer groups of healthy Zaandam guests to Rotterdam, with strict protocols for this process developed in conjunction with the U.S. Centers for Disease Control and Prevention," the representative said. "Only those who have not been ill will be moved, and health screenings will be conducted before transferring. Priority for the first guests to transfer will be given to those on Zaandam with inside staterooms and who are over 70."

The leaked memo said that ports and airports in South America and Central America had been closed off to the Zaandam and that "colleagues, fleet family members, and guests" on board "are in dire need."

There were originally 1,243 guests and 586 crew members on the Zaandam. The ship's passengers have been confined to their staterooms since Sunday, with crew members delivering meals and collecting trash from cabins.

A view of the MS Rotterdam from a passenger on board the MS Zaandam. Courtesy of a Zaandam Passenger

The memo described a plan to sail the Rotterdam northwest, up to the United States, predicting that it could reach San Diego in about a week depending on its "fuel and provisions supply." From there, the Rotterdam would "disembark all guests and fly them home."

Only "well guests" — anyone "showing no signs of illness, including fever" — would be eligible for the ship transfer. Sick guests and their "close contacts" would remain behind on the Zaandam. The document did not specify a plan for healthy Zaandam crew members.

The memo said that members of the Zaandam's crew "are showing influenza-like symptoms, such as fever and cough." Business Insider reported on Thursday that, based on conversations with Zaandam passengers, at least 86 crew members and 58 guests had fallen ill.

The Rotterdam would give its sister ship medical staff, supplies, equipment, and "a number of COVID-19 test kits for use in identifying whether or not the illness is on board," the memo said.

Passengers would be transferred to the Rotterdam through a "secure corridor" that would "take them directly to their staterooms," the memo said. Under that plan, no crew members from the Rotterdam would "come into close contact with anybody transferred and en route to their stateroom." All rescued guests would be required to "stay in isolation in their staterooms" for the duration of the journey, and meals would be provided through contactless delivery.

The memo said that the Rotterdam crew would have enough surgical masks and gloves for the estimated seven-to-10-day voyage up to the United States. It said that personal protective equipment would be "provided to wear based on their individual risk," singling out at-risk teams like medical, hotel, technical, and deck staffers.

'We are mariners'

Rotterdam crew members have told Business Insider that despite the memo's attempts to quell their fears, they are frightened of becoming sick. They said they felt that Holland America left them without much of a choice.

"Our crew do not agree, and they did not give us any choice about it," one crew member said. "We will have to serve guests possibly infected by COVID-19 without any equipment or instruction."

The crew member said Holland America "did not care for the health of our crew" by tasking the Rotterdam with the mission.

The memo also repeatedly addressed crew members' concerns about safety.

"The chances that anyone will become ill from well guests is very low," it said. "There is a higher chance of becoming ill traveling through an airport to get home than there is on the ship." It also said that once at the port in the United States, the "well guests" would be "allowed to freely disembark go to a hotel or fly home with no restrictions."

"These guests are healthier than most people who travel, sail, and fly every day," the memo said, adding that crew members had a greater likelihood of being exposed to illness on their international flights home.

The document also provided Rotterdam crew members a statement to give to family members. It described the transfer as "part of a humanitarian crisis mission in which the Rotterdam team is coming to the rescue of the Zaandam guests and crew."

Rotterdam crew members uncomfortable with the mission ought to "let us know how you feel and what your concerns honestly are," the memo said.

"We should mention that nobody will be asked to do something that they don't want to do," the memo said. "But we would like you to think about your fellow team members on board Zaandam and the guests who are elderly and need your help, and what one would hope they would do for the Rotterdam team if you ended up in the same situation — as that could have been easily been the case."

It added: "Again, nobody will be pushed to do something that doesn't feel right to them."

The memo offered an explanation for why Rotterdam crew members were not kept more aware of the nature of their mission, saying the situation on the Zaandam "escalated very rapidly."

"We are mariners, and we consider this our duty and our obligation, and so in the tradition, we are proceeding with helping our sister ship the Zaandam," the captain of the Rotterdam said in the leaked audio. "Our guests and our fellow crew members on board need us. There are no easy choices here. In order to protect the Zaandam guests and crew members, we need to move guests to the Rotterdam."

Read Holland America's full statement:

Zaandam is currently off the coast of Panama and rendezvoused with sister ship Rotterdam at 7:30 p.m. local time yesterday, March 26. We received approval from Panamanian authorities to conduct ship-to-ship operations at anchor between the two vessels. Medical supplies and additional medical staff were transferred to Zaandam.

Today we announced a plan to transfer groups of healthy Zaandam guests to Rotterdam, with strict protocols for this process developed in conjunction with the U.S. Centers for Disease Control and Prevention (CDC). Only those who have not been ill will be moved, and health screenings will be conducted before transferring. Priority for the first guests to transfer will be given to those on Zaandam with inside staterooms and who are over 70. Once aboard Rotterdam, all guests will continue to remain in their staterooms until disembarkation. Any guests who are currently ill, or in isolation as a close contact, and all crew will remain on Zaandam.

While the onward plan for both ships is still being finalized, we continue to work with the Panamanian authorities on approval to transit the Panama Canal for sailing to Fort Lauderdale, Florida.

Yesterday a number of patients with respiratory symptoms were tested for COVID-19 and two individuals tested positive. Out of an abundance of caution, on March 22 when Zaandam first saw a number of guests reporting to the medical center with influenza-like illness symptoms, we took immediate protective measures, including asking all guests to self-isolate in their staterooms and implementing all other appropriate precautions that have been developed in coordination with the CDC. All guests and crew received face masks yesterday and were provided with instructions on when and how to wear them.

Currently, 53 guests (4%) and 85 crew (14%) have reported to Zaandam's medical center with influenza-like illness symptoms. There are 1,243 guests and 586 crew on board. On Zaandam there are four doctors and four nurses. On Rotterdam there are two doctors and four nurses.

Holland America Line can confirm that four older guests have passed away on Zaandam. Our thoughts and prayers are with their families and we are doing everything we can to support them during this difficult time.

Complimentary telephone counseling services from our care partner, Empathia, have been made available to guests and crew if they would like extra support during this time. For those with family members on board, they can call the following numbers for information: 877-425-2231 or 206-626-7398.

Zaandam was sailing a South America cruise that departed Buenos Aires, Argentina, on March 7 and was originally scheduled to end at San Antonio, Chile, on March 21. Due to global health concerns, Holland America Line made the decision to suspend its global cruise operations for 30 days and end its current cruises in progress as quickly as possible so guests could return home. No one has been off the ship since March 14 in Punta Arenas, Chile.

Are you a cruise ship passenger or employee with a story to share? Email acain@businessinsider.com.