A woman working as a tour-bus guide in Japan has tested positive for the coronavirus for a second time, Osaka's prefectural government said, the first known person in the country to do so amid growing concerns about the spread of the infection.

The second positive test comes as the number of confirmed cases in Japan rose to 186 by Thursday from around 170 the day before. Tokyo has urged big gatherings and sports events be scrapped or curtailed for two weeks to contain the virus while pledging the 2020 Olympic Games will still go ahead in the city.

The 186 cases reported by Japan's health ministry are separate from 704 reported from an outbreak on the Diamond Princess cruise liner that was quarantined off Tokyo earlier this month. A total of seven people have died, including four from the ship.

Though a first known case for Japan, second positive tests have been reported in China, where the disease originated late last year. The outbreak has spread rapidly and widely, infecting about 80,000 people globally and killing nearly 2,800, the vast majority in mainland China.

The woman, a resident of Osaka, in western Japan, tested positive on Wednesday after developing a sore throat and chest pains, the prefectural government said in a statement, describing her as being in her forties. She first tested positive in late January and was discharged from hospital after recovering on Feb. 1, according to the statement.

Health Minister Katsunobu Kato said in parliament the central government would need to review patient lists and keep tabs on the condition of those previously discharged, as health experts analyzed the implications of testing positive for the virus after an initial recovery.

"Once you have the infection, it could remain dormant and with minimal symptoms, and then you can get an exacerbation if it finds its way into the lungs," said Philip Tierno Jr., Professor of Microbiology and Pathology at NYU School of Medicine.

Tierno said much remains unknown about the virus. "I'm not certain that this is not bi-phasic, like anthrax," he said, meaning the disease appears to go away before recurring.

Asked to comment on prospects for the Olympic Games going ahead in Tokyo this summer, Tierno said, "The Olympics should be postponed if this continues ... There are many people who don't understand how easy it is to spread this infection from one person to another."

Japan has changed its strategy in combating the contagion, seeking to slow its spread and minimize the number of deaths. Public broadcaster NHK said the crew of the Diamond Princess would begin disembarking on Thursday, and those with no symptoms would remain at a facility near Tokyo for further monitoring.

As part of the attempts to contain the outbreak, Tokyo Olympics officials are considering scaling down the torch relay, Tokyo 2020 CEO Toshiro Muto said on Wednesday.

The government is also considering scaling back this year's March 11 memorial ceremony for victims of 2011's massive earthquake and tsunami, Chief Cabinet Secretary Yoshihide Suga told reporters on Thursday.