Tourists on a sightseeing cruise ship wave to passengers of the cruise ship Diamond Princess, which is anchored at Daikoku Pier Cruise Terminal in Yokohama

TOKYO - Another 39 people have tested positive for the coronavirus on the cruise ship Diamond Princess quarantined in Japan, with one quarantine officer also infected, bringing the total to 175, the health ministry said on Wednesday.

The Diamond Princess was placed in quarantine for two weeks upon arriving in Yokohama, south of Tokyo, on February 3, after a man who disembarked in Hong Kong was diagnosed with the virus.

The epidemic originated in mainland China, where more than 1,100 people have now died of the virus.

About 3,700 people are on board the ship, which usually has a crew of 1,100 and a passenger capacity of 2,670. 

The ministry said tests were being conducted for others deemed to need them and it would announce the results later.

The British-flagged Diamond Princess is managed by Princess Cruise Lines, one of the world's largest cruise lines and a unit of Carnival Corp.

Kyodo news agency, citing the health ministry, said that of the 39 cases, 10 were crew and 29 were passengers.

Ten were Japanese nationals and the others were from 11 countries, including the United States and China. Four were in serious condition, Health Minister Katsunobu Kato said.

People who test positive for the virus are taken off the ship to a hospital.

The quarantine officer who was infected had been handing out questionnaires checking the health of passengers and crew since February 3, and had been following rules that require the wearing of a mask and gloves but not a full protective suit, according to the Nikkei business daily, quoting the health ministry.

"It's terrible about the quarantine officer," one passenger on the ship, who declined to be identified, told Reuters.

"The ones who came to our room to do the initial screening had gloves and surgical masks, while the ones who came to do the actual virus test also had full gowns and full face masks."

'HIGH RISK'

A health ministry official had no immediate comment, but Nikkei said the ministry was checking the officer's contacts with colleagues and family members.

Mark Kortepeter, a professor of epidemiology at the University of Nebraska Medical Center, said that although it was hard to reach conclusions based on limited information, the ship infections pointed to an "agent that is highly transmissible," at least in enclosed environments.

"The infected quarantine officer probably indicates the high risk, even for individuals who are trying to protect themselves, because the virus is unforgiving and there is no room for error in use of personal protective equipment and hand hygiene," he said. "A small number of virus particles is likely needed to infect, making it an efficient spreader."

The government was considering allowing elderly and those with chronic illnesses to disembark before the February 19 target date for the end of quarantine, some media reported, but added it would take time to determine where they could be sent.

About 80% of the passengers were aged 60 or over, with 215 in their 80s and 11 in the 90s, the English-language Japan Times newspaper reported.

An improvement in life for people on the boat came several days ago with the announcement they can receive packages sent to the address of the pier - a service that Rob Thomson, a New Zealander living in northern Japan, whose parents are on the boat, made prompt use of.

"The one thing that they were missing were hot drinks during the day - they were getting coffee or tea at breakfast, but then during the day it was cold water or Coca-Cola or soft drinks ... and Dad was saying he'd like fresh fruit other than apples or oranges," he said, adding that he placed an order Tuesday night.

"So I tried sending some grapes and strawberries and stuff. And apparently the fresh things have already been delivered to somebody on the dock."

The foreign ministry released a notice on Wednesday urging its nationals to consider delaying trips to China and for Japanese in China to return home.

Japan has sent four chartered flights to China's Hubei province, the epicentre of the outbreak, for its citizens there to return, and plans a fifth. The people who returned on the first flight will be released on Wednesday if they test negative for the virus, media said.

Reuters