As the worst-hit areas of Asia continued to struggle with a viral epidemic, with hundreds more cases reported in South Korea and China, worries about infection and containment spread across the globe.
For the first time, the coronavirus has caused more new cases outside China, the epicentre of the outbreak, than inside the country.
With Brazil on Wednesday confirming Latin America's first case, the virus has reached every continent but Antarctica.
The United States, which has 60 cases, hasn't been spared the fear that has swept Asia, Europe and the Mideast.
US President Donald Trump declared the US was "very, very ready" for whatever threat the coronavirus brings, and he put Vice President Mike Pence in charge of overseeing the country's response.
As the epidemic expanded geographically, worries about the COVID-19 illness multiplied.
"The sudden increases of cases in Italy, the Islamic Republic of Iran and the Republic of Korea are deeply concerning," WHO director-general Tedros Adhanom Ghebreyesus said.
Though the virus has pushed into countries both rich and poor, its arrival in places with little ability to detect, respond and contain it brought worry that it could run rampant there and spread easily elsewhere.
Major gatherings have been eyed warily, with schools closing, churches moving services online, food deliveries booming and many business conferences and sporting events cancelled.
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The Olympics begin July 24 in Tokyo, and Japan's top government spokesman said preparations would proceed and the games would go on as planned.
South Korea reported 505 more cases on Thursday, bringing its total to 1766.
China reported 433 new cases along with 29 additional deaths. Thursday's updates bring mainland China's totals to 78,497 cases, and 2744 deaths.
China has put Wuhan and nearby cities on lockdown, many airlines have reduced Chinese flights, and many places have increased monitoring of arrivals from China, all resulting in far few Chinese arrivals around the globe.
In Europe, an expanding cluster of more than 440 cases in northern Italy was eyed as a source for transmissions.
In the Middle East, blame was directed at Iran, which had 19 deaths, the highest toll outside China. Saudi Arabia said early Thursday it would ban tourists from places with confirmed outbreaks, including pilgrims coming for the Umrah or to visit the Prophet's Mosque in Medina.
Shortly after Trump spoke about US efforts on the virus, health officials identified what could be the first community spread US case. The patient in California was not known to have travelled to a country with an outbreak or had ties to a known patient. Most of the previously confirmed US cases had travelled to China, were evacuated from the virus-stricken Diamond Princess cruise ship, or were family members of those cases.
After many countries restricted travel from China to try to prevent the illness from spreading, China itself is now heavily regulating arrivals from abroad.
State broadcaster CCTV reported South Koreans were being monitored after Chinese authorities detected fevers in five arrivals.