According to Japanese health authorities, at least 10 people on board the Diamond Princess cruise ship docked in the port of Yokohama have tested positive for coronavirus.
Almost 300 of the 3,700 people on the cruise ship have been tested so far. The number of infected could rise.
The checks began after an 80-year-old Hong Kong man who had been on the ship last month fell ill with the virus.
Some 3,600 people on a second cruise ship docked in Hong Kong are also being tested.
Chinese health authorities are stepping up efforts to control the spread of the virus, with approximately 18 million people in the east of the country now required to stay at home.
In Wuhan, the epicenter of the virus, 11 large public venues including sports arenas are being turned into makeshift hospitals to provide an additional 10,000 beds for the sick. Two new hospitals have already been built there since the outbreak started.
President Xi Jinping said China’s preventive measures were “achieving a positive effect”, state media reported. He said China was confident and capable of winning the war against the virus, after authorities were criticized for their initial handling of the outbreak.
The World Health Organization (WHO) has declared a global health emergency over the outbreak but said it did not yet constitute a “pandemic”, or the worldwide spread of a new disease.
However, the number of cases in China jumped by nearly 4,000 on February 4 alone to more than 24,300, with another 65 deaths bringing the total to 490.
The new coronavirus causes severe acute respiratory infection and symptoms usually start with a fever, followed by a dry cough. Most people infected are likely to fully recover – just as they would from a flu.
There is a much smaller number of cases in countries around the globe other than China – two people outside of mainland China have died of the disease.
The Hong Kong man believed to be the source boarded the cruise ship in Yokohama, Japan, on January 20, and disembarked in Hong Kong on January 25. He was only later found to have tested positive for the virus.
Officials on the cruise ship began screening guests on February 3, and the vessel was placed under quarantine on February 4.
Passengers and crew on the ship will now be under quarantine for 14 days. The incubation period of the virus is believed to be around two weeks.
All 10 cases are in those over the age of 50 and one is in their 80s, Japanese broadcaster NHK said.
Two of them are said to be Japanese, and none are in “serious condition”, it added.