A public health emergency has been declared in the US over the spread of the coronavirus and said it would deny entry to any foreign nationals who have visited China in the past two weeks.

According to authorities, US citizens returning from Hubei province, where the outbreak started, will be quarantined for two weeks.

Nearly 10,000 cases of the new virus have been confirmed, most of them in China, since it emerged in December.

More than 100 cases have been reported outside China, in 22 countries.

On January 31, Beijing said the death toll had risen by 45 to 258 – all of them in China and 249 in Hubei.

Earlier, it emerged that the number of new coronavirus cases worldwide had overtaken that of the SARS epidemic, which spread to more than two dozen countries in 2003.

There were around 8,100 cases of SARS – severe acute respiratory syndrome – during the eight-month outbreak. In total, 774 people were killed by SARS.

On January 30, the World Health Organization (WHO) declared a global health emergency over the new outbreak.

WHO spokesman Chris Lindmeier warned that closing borders could in fact accelerate its spread, with travelers entering countries unofficially.

“As we know from other scenarios, be it Ebola or other cases, whenever people want to travel, they will. And if the official paths are not opened, they will find unofficial paths,” he said.

He said the best way to track the virus was at official border crossings.

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In a public statement on January 31, Health Secretary Alex Azar said US citizens returning from Hubei province would face 14 days of quarantine while those returning from other parts of China would be allowed to monitor their own condition for a similar period.

He told reporters: “Following the World Health Organization decision, I have today declared that the coronavirus represents a public health emergency in the United States.”

Citing the need to relieve pressure on authorities, Alex Azar said that foreign nationals who had travelled in China in the past two weeks would be denied entry to the US.

He added: “The risk of infection for Americans remains low and with these, and our previous, actions we are working to keep the risk low.”

Another confirmed case in the US on January 31 – in California – brought the number there to seven. Robert Redfield, director of the Centers for Disease Control and Prevention (CDC), said 191 people were under observation for the disease.

The US announcement came as other countries around the world scrambled to contain the spread of the new virus, 2019-nCov.

On January 31, the UK confirmed its first two cases.

Estimates by the University of Hong Kong suggest the true total number of cases could be far higher than official figures suggest. Based on mathematical models of the outbreak, experts there say more than 75,000 people may have been infected in the city of Wuhan alone, where the virus first emerged.

Most cases outside China involve people who have been to Wuhan. Germany, Japan, Vietnam, the US, Thailand and South Korea have reported person-to-person cases – patients being infected by people who had travelled to China.

Meanwhile in Wuhan, voluntary evacuations of hundreds of foreign nationals are under way.

Australia, South Korea, Singapore, New Zealand and the UK are expected to quarantine all evacuees for two weeks to monitor them for symptoms and avoid contagion.