Transcript for Amid global panic over coronavirus, thousands quarantined on cruise ship in Japan

We had such a great time. Reporter: It was supposed to be the dream honeymoon for newlyweds ma Lenna basso and guy serulo. I was thinking of canceling the trip a little early because we were getting the coronavirus and everything like that. And they were like no, we're halfway across the world, stick it out. Reporter: A 30-day cruise around Asia on the "Diamond princess," seen in all its glory in this promotional video. And it was just about to come to an end. What day were you supposed to disembark? 12 hours literally after they told us we were quarntded. 12 hours. You were so close. I tried to go get coffee. It was like a quarter to 7:00. And all the staff was like report to your room. Reporter: Now Malena and guy and almost 3,700 others aboard the cruise okd docked south of Tokyo are one of the largest clusters of coronavirus cases outside mainland China. The number of passengers affected doubling to 135, including 23 Americans. Guests aboard the boat are being quarantined for at least 14 days. They're being asked to take their temperature every two to three hours. They only have access to the above deck for fresh air once every four days. We've been skyping with people on board to see what life is like including newly retired couple John and Melanie Haren who are quarantined in a cabin without windows. This is the first time we've been outside in the sun, and it's beautiful. Today's day six, and we're almost over the hump. Reporter: But on day seven of their quarantine their worst fear. The couple telling us John was burning up with a 103 degree fever. They say they're waiting for help. He got a great big bucket of ice, and then we're doing cold compresses on John. His fever is now 103 again. Just trying to keep him cool and comfortable. He's burning up. And just have prayers for him. We know not just with coronavirus but many respiratory infections have a higher likelihood of spread with people in close quarters. Reporter: Across China, where it's believed the outbreak began, chilling scenes. A man collapsed on the street. Quarantine teams seen dragging a couple from their apartment after they reportedly refused to self-quarantine. Ground zero of the epidemic, Wuhan, China, where the virus was traced to an animal market. Now the city of 11 million is like a ghost town. The world health organization issuing a warning about the virus's spread. The detection of this small number of cases could be the spark that becomes a bigger fire. Reporter: Officials say more than 40,000 people worldwide have been confirmed with the new coronavirus. Nearly all in mainland China. Most cases have been mild. But more than 1,000 people have died. The death toll surpassion the sars outbreak of 2002. Sars was a type of coronavirus. Mers was also a type of coronavirus. They got a lot of attention because they spread from their country of origin and had very high fatality, mortality rates. Reporter: Experts say the novel coronavirus typically causes flu-like symptoms of fever and cough. Once it was determined that the transmission of this virus could go person to person, it upped the ante, if you will, in terms of its likelihood of becoming a pandemic. Reporter: With global concern growing, the Chinese government expanding its efforts to contain the virus. State TV documented the construction of two hospitals in just over a week. And a convention center convert Ed into a massive quarantine center for thousands. On Friday the 34-year-old Chinese doctor who raised the alarm about the coronavirus died from the outbreak he warned the world about. Only one American is known to have died from the coronavirus, and that was in China. Still, the question remains whether the virus poses a serious threat in the U.S. With at least 13 confirmed cases and many more under investigation. One thing we can do very efficiently here in the united States is tracing contacts, finding out where someone's been, who they've come in contact with, and then following up with those individuals to make sure that they don't develop symptoms. Reporter: Military bases across the country are serving as quarantine centers. March air reserve base in Riverside, California, 195 passengers who were recently in China are now on. So we just got the news that we're going to be quarantined here for 14 days. Reporter: The future of this new coronavirus still remains uncertain. As countries try to contain the spread while scientists are making progress toward a new vaccine. The great news with this coronavirus outbreak is that the Chinese got the DNA sequence of this coronavirus and released that to the world very, very early on. Reporter: Tonight back on board the "Diamond princess" nerves are high as guests are waking up to their eighth day in quarantine and uncertain how much longer they'll have to wait. It's scary hearing the numbers increase. But then the embassy e-mailed me back. They're like oh, on February 19th you'll be released. But it's like we're still scared. Like god forbid anything like -- what if they say no, you're stuck here. Reporter: For "Nightline" I'm Maggie Rulli in Yokohama, Japan.

This transcript has been automatically generated and may not be 100% accurate.