Another 41 people on a cruise ship quarantined off Japan have the new coronavirus, the country's health minister said Friday, confirming more on board will now be tested for the illness.

The newly diagnosed infections mean at least 61 people from the ship have contracted the virus, which has killed hundreds of people, most of them in China, and infected more than 30,000 on the mainland.

Japanese authorities have so far tested 273 people on board the Diamond Princess, which was quarantined after a former passenger, who disembarked in Hong Kong last month, was diagnosed with the virus.

"The results of the remaining 171 tests came out and 41 tested positive," Health Minister Katsunobu Kato told reporters.

"Today they will be sent to hospitals in several prefectures, and we are now preparing for that."

"In total, out of 273 specimens, 61 tested positive," he added.

The newly diagnosed include 21 Japanese, as well as Americans, Canadians, Australians, an Argentine and a Briton.

There were more than 3,700 passengers and crew on the ship when it arrived off Japan's coast on Monday evening. It docked in Yokohama on Thursday to resupply for a quarantine that could last until February 19.

Twenty people who were earlier diagnosed with the virus have already been removed from the vessel, including one who is in serious condition, a health ministry official said, without providing further details.

Testing was initially carried out on those who displayed symptoms or had come into close contact with the former passenger diagnosed with the virus.

But Kato suggested testing would now be expanded.

Authorities will "test those who are susceptible to illness, including elderly people and those with other ailments, as well as those who had close contact with the people newly diagnosed with the virus," he said.

There were no immediate details on how many people would meet those criteria or when the testing might take place.

- 'I want to cry' -

Japan has already reported at least 25 cases of coronavirus aside from the infections on board the ship, and evacuated hundreds of citizens from Wuhan, the Chinese city where the virus emerged.

A fourth evacuation flight carrying both Japanese citizens and non-Japanese spouses and those with other ties to the country arrived on Friday morning.

Japanese authorities have said the ship's quarantine may last until February 19, with passengers required to stay inside their cabins in a bid to prevent new infections.

Those on board have described their confusion and frustration as their luxury cruise descends into a nightmare.

"Just woke up from (a) sleepless night," wrote Yardley Wong, a Twitter user on board the ship.

"Getting so emotional... I want to cry."

David Abel, a British passenger who has been posting videos from the ship, said people were hearing information from media more quickly than authorities on board.

"It's not right. It's so unfair," he said.

But he praised the efforts of crew members who are now struggling to deliver meals to thousands of passengers in their cabins.

Those with inside cabins, which have no windows, have been allowed onto decks in small groups to get fresh air, but under strict conditions, including wearing a mask at all times when out of their rooms.

"The quarantine officials require that you avoid congregating in large groups and maintain a separation of at least one metre from each other when talking," the ship's captain said in an announcement on Friday morning.

"We require that you wear as a minimum, warm clothing, hat and a scarf if possible," he added.

A second cruise ship carrying a passenger suspected of infection with coronavirus will not be allowed to dock in southern Japan, the government said Friday.