World health officials have expressed concern that the coronavirus is spreading between people outside China.

The new virus has now infected more people in China than fell ill during the 2002-2003 severe acute respiratory syndrome (Sars) outbreak. The number of cases has jumped to 7,711, surpassing the 5,327 people diagnosed with Sars.

The death toll, which rose to 170 on Thursday morning, is lower than the 348 people who died in China from Sars. Scientists say there are still many questions to be answered about coronavirus, including how easily it spreads and how severe it is.

The World Health Organisation’s (WHO) 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 remains centred in the city of Wuhan and in Hubei province but that “information is being updated and is changing by the hour”.

Mr 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 Tedros Adhanom Ghebreyesus has reconvened an expert committee to meet on Thursday. It will assess whether the outbreak should be declared a global emergency.

The first cases in the Middle East have been confirmed as a family-of-four from Wuhan that was visiting the United Arab Emirates.

Australia and Singapore are among the countries reporting new cases, as the number outside China topped 70. The vast majority are people who came from Wuhan.

To date, about 99% of cases are in China. Mr Ryan estimated the death rate of the new virus at 2%, 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 is likely many milder cases of the virus are being missed.

In comparison, the Sars virus killed about 10% of people who caught it.

WHO officials, from left, Tedros Adhanom Ghebreyesus, Michael Ryan and Maria van Kerkhove
WHO officials, from left, Tedros Adhanom Ghebreyesus, Michael Ryan and Maria van Kerkhove (Martial Trezzini/Keystone via AP)

Mr Ryan noted there were several aspects of the new virus outbreak that are 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 is 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 as other countries planned similar evacuations from the city of Wuhan, which authorities have shut down to try to contain the virus.