World health officials, back from a visit to Beijing, expressed great concern that a dangerous new virus was spreading between people outside of China, even as the number of illnesses continue to grow dramatically inside that Asian nation.
The new virus has now infected more people in China than were sickened during the 2002-2003 severe acute respiratory syndrome (SARS) outbreak. On Wednesday, the number of cases jumped to 5974, surpassing the 5327 people diagnosed with SARS.
The death toll, which stood at 132 on Wednesday, is lower than the 348 people who died in China from SARS.
Doubts have been raised about the official death toll, however, with claims Chinese authorities have been cremating bodies in secret.
Chinese-language news outlet Initium interviewed people working at local cremation centres in Wuhan, who said bodies were being sent directly from hospitals without being properly identified and added to the official record.
"So there are reasons to remain sceptical about what China has been sharing with the world because while they have been more transparent about certain things related to the virus, they continue to be sketchy and unreliable in other aspects," said DW News East Asia correspondent William Yang.
Scientists say there are still many questions to be answered about the new virus, including just how easily it spreads and how severe it is.
The World Health Organisation's emergencies chief told reporters that China was taking "extraordinary measures in the face of an extraordinary challenge" posed by the outbreak.
Dr Michael Ryan spoke at a news conference after returning from a trip to Beijing to meet with Chinese President Xi Jinping and other senior government leaders.
He said the epidemic remained centred in the city of Wuhan and in Hubei province, but "information is being updated and is changing by the hour".
Dr Ryan said the few cases of human-to-human spread of the virus outside China – in Japan, Germany and Vietnam – were part of the reason the UN health agency's director-general has reconvened an expert committee to meet on Thursday.
It will assess whether the outbreak should be declared a global emergency. To date, about 99 per cent of the nearly 6000 cases are in China.
Dr Ryan estimated the death rate of the new virus at 2 per cent but said the figure was very preliminary. With fluctuating numbers of cases and deaths, scientists are only able to produce a rough estimate of the fatality rate, and it's likely many milder cases of the virus are being missed.
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In comparison, the SARS virus killed about 10 per cent of people who caught it. The new virus is from the coronavirus family, which includes those that can cause the common cold as well as more serious illnesses such as SARS and Middle East respiratory syndrome (MERS).
Dr Ryan noted there were several aspects of the new virus outbreak that were extremely worrying, citing the recent rapid spike in cases in China. He said that while scientists believe the outbreak was sparked by an animal virus, it's unclear if there are other factors driving the epidemic.
"Without understanding that, it's very hard to put into context the current transmission dynamics," he said.
Meanwhile, countries began evacuating their citizens from the Chinese city hardest hit by the virus.
Chartered planes carrying about 200 evacuees each arrived in Japan and the United States early on Wednesday as other countries planned similar evacuations from the city of Wuhan, which authorities have shut down to try to contain the virus.
The first cases in the Middle East were confirmed on Wednesday, a family of four from Wuhan that was visiting the United Arab Emirates. Airlines around the world announced they were cutting flights to China, and Hong Kong was suspending rail travel to and from the mainland at midnight.
The number of cases in China rose 1459 from the previous day, a smaller increase than the 1771 new cases reported on Tuesday.
Australia and Singapore were among those reporting new cases, as the number outside China topped 70. The vast majority are people who came from Wuhan.
Four passengers on the evacuation flight to Japan had coughs and fevers, and two were diagnosed with pneumonia.
It wasn't clear whether they were infected with the new virus, which first appeared in Wuhan in December. Its symptoms, including cough and fever and in severe cases pneumonia, are similar to many other illnesses.
Takeo Aoyama, an employee at Nippon Steel Corp's subsidiary in Wuhan, told reporters he was relieved to be able to return home.
"We were feeling increasingly uneasy as the situation developed so rapidly and we were still in the city," Mr Aoyama said, his voice muffled by a white surgical mask.
A US plane from the Chinese city at the centre of the outbreak arrived in California after a refuelling stop in Alaska. All 201 passengers, who included diplomats from the US Consulate in Wuhan, passed health screenings in China and Anchorage.
Australia, New Zealand and Britain were among the latest countries to announce they are planning evacuations.
British health secretary Matt Hancock tweeted that "anyone who returns from Wuhan will be safely isolated for 14 days, with all necessary medical attention".
The measures are a step up from those during the devastating 2014-16 ebola outbreak when returning travellers from West Africa were asked to monitor themselves for symptoms.
Mark Woolhouse, a professor of infectious disease epidemiology at the University of Edinburgh, said the steps were justified to prevent the introduction of the virus and its spread.
"There's always a balance between the draconian measures of public health and what people might want to do, and obviously it's regrettable if people who turn out not to have the virus are quarantined unnecessarily," he said.
The outbreak has affected international sporting events. The International Hockey Federation postponed Pro League games in China, and soccer, basketball and boxing qualifiers for the Tokyo Olympics in February have been moved outside of the country.
In China's Hubei province, 17 cities including Wuhan have been locked down, trapping more than 50 million people in the most far-reaching disease control measures ever imposed.
Sara Platto, an Italian animal behaviour researcher and veterinarian, said there were 25 Italians stuck in Wuhan who stay in touch online for material and emotional support.
"My son turned 12 on January 23, the first day of the lockdown in Wuhan. So he couldn't invite his friends over. We had a remote birthday celebration, with people 'visiting' him over WeChat," Ms Platto said, referring to a Chinese messaging app. "We called it the epidemic birthday."
The source of the new virus and the full extent of its spread are still unknown. However, the World Health Organisation said most cases reported to date "have been milder, with around 20 per cent of those infected experiencing severe illness".
Scientists expect many crucial questions about the virus' behaviour will be answered in the coming weeks as the outbreak evolves and it becomes clearer how people are infected.
Although the Chinese health minister and others have suggested the virus is spreading before people get symptoms, data to confirm that has not yet been shared widely beyond China.
"It's still unclear whether that takes place," said Malik Peiris, chair in virology at the University of Hong Kong.
If it does, that might explain why China has already exceeded the case numbers for SARS.
"The fortunate thing about SARS, if there was anything fortunate, was that transmission did not take place before symptoms," he said.
Mr Peiris said if it turned out that the new coronavirus could indeed be spread by people who didn't show any symptoms, "a pandemic is a scenario that we have to consider".