Japan has reported its first case of a person becoming reinfected with the coronavirus after appearing to have fully recovered.
Officials in Osaka confirmed that a woman who works as a tour bus guide had tested positive for COVID-19 for the second time, further heightening concerns about the spread of the infection in the country.
It came as other nations stepped up measures in response to the outbreak, with Iran banning Chinese citizens from entering the country after it confirmed it had 245 confirmed cases of the coronavirus - and 26 deaths.
:: Listen to the Daily podcast on Apple Podcasts, Google Podcasts, Spotify, Spreaker
There are now 189 confirmed cases of the flu-like illness in Japan, excluding the 639 on the Diamond Princess cruise ship that was docked for two weeks at Yokohama, and a third death was reported on Wednesday.
While there have been a number of cases of reinfection in China, notably in Wuhan province where the coronavirus outbreak originated late last year, second positive tests have not been reported elsewhere in the world.
The woman in Osaka, western Japan, who is in her 40s, tested positive on Wednesday after developing a sore throat and chest pains.
She was first diagnosed with COVID-19 in late January and was discharged from hospital on 1 February, and her reinfection has health experts worrying that the illness could remain dormant after an apparent recovery.
Philip Tierno Jr, professor of microbiology and pathology at New York University, said: "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."
Prof Tierno said the 2020 Olympic Games due to take place in Tokyo this summer "should be postponed" if the outbreak continues, although officials have insisted it will still go ahead as it stands.
In other developments around the world:
- The UK has confirmed two new cases of COVID-19, taking the national total to 15
- Around 160 British tourists are in lockdown at a Tenerife hotel over coronavirus fears
- Stock markets are falling sharply again as countries report a surge in coronavirus cases
- Some UK hospitals and other medical sites including GP surgeries will now test flu patients for the virus
- The government has banned the export of an HIV drug and anti-malaria infection treatment so that they can be tested as potential treatments for COVID-19
- Donald Trump has appointed his vice president Mike Pence to lead the US response to the coronavirus
- Saudi Arabia has halted the entry of Muslim pilgrims to the holy cities of Mecca and Medina
- Russia's Federal Tourism Agency recommends the country's holiday firms suspend tours to Italy, South Korea and Iran until outbreaks are brought under control
- South Korea has reported 334 more cases, bringing its total to 1,595 - the second-highest number after China
- China reports 433 new cases, 383 in the city of Wuhan, where the disease emerged in December
Japanese Prime Minister Shinzo Abe has called for sports and cultural events to be scrapped or curtailed for two weeks in the battle to stem the virus, describing the next fortnight as "crucial" in the country's bid to contain it.
He has called on people to avoid large gatherings, prompting major tourist and visitor destinations in the Japanese capital to introduce extra health and safety measures.
Disney's Tokyo theme parks will require all staff to wear face masks from Friday, while a popular museum dedicated to Japanese animation house Studio Ghibli has been completely shut until 17 March.
The PM has also asked all schools to remain closed through the country's spring break, ahead of the start of the new term at the beginning of April
Health minister Katsunobu Kato has said in parliament that the government will also be reviewing patient lists to keep tabs on the condition of other COVID-19 patients who have been discharged.
According to experts at Johns Hopkins, who are tracking the outbreak from the US, Japan ranks fourth on the list of countries with the most cases of coronavirus - again excluding the Diamond Princess.
The vast majority of the 82,171 cases are in China, followed by South Korea with 1,595 and Italy with 453.
The figures were up to date as of 9.53am UK time on Thursday.