Chinese authorities have moved to lock down multiple cities, home to more than 23 million people, in an unprecedented effort to contain the deadly coronavirus.

The respiratory virus has claimed 18 lives since emerging from a seafood and animal market in the central city of Wuhan, infected at least 647 people nationwide and been detected as far away as the United States.

The deadly virus claimed its first victim outside the epicentre of the outbreak, with authorities reporting a death in Hebei province, near Beijing.

The victim, aged 80, died on Wednesday but the cause was not confirmed until Thursday (CST), the South China Morning Post reports.

The other 17 deaths occurred in Hubei province, the epicentre of the contagion.

Yi Guan, a prominent virologist, warned the virus showed signs of being far worse than severe acute respiratory syndrome (SARS) after travelling to Wuhan.

"Conservative estimates suggest that the scale of infection may eventually be 10 times higher than SARS," he said.

In 2002-03 SARS infected more than 8000 people, killing 774.

Eight cities in Hubei – Wuhan, Huanggang, Ezhou, Chibi, Xiantao, Qianjiang, Zhijiang and Lichuan – are now subject to travel bans, according to notices released by local governments in the province.

Outbound trains and planes in Wuhan were indefinitely suspended. Tollways on roads out of the city were closed as well. In Huanggang, theatres, internet cafes and other entertainment centres were also ordered closed.

Police, SWAT teams and paramilitary troops guarded Wuhan's train station, where metal barriers blocked the entrances this morning. Only travellers holding tickets for the last trains out were allowed to enter. Normally bustling streets, shopping malls, restaurants and other public spaces in the city of 11 million people were eerily quiet.

In addition to shutting down the train station, authorities closed the airport and halted ferry, subway and bus service.

China will also close Beijing's Forbidden City – one of the country's most revered cultural sites – due to rising fears over the new SARS-like virus.

The sprawling imperial palace will close on Saturday until further notice to "avoid cross-infection caused by the gathering of people," it said in an online statement.

Chinese officials have not said how long the shutdowns will last. While sweeping measures are typical of China's communist government, large-scale quarantines are rare around the world, even in deadly epidemics, because of concerns about infringing on people's liberties. And the effectiveness of such measures is unclear.

'NOT A GLOBAL EMERGENCY'

The World Health Organization decided against declaring the outbreak a global emergency for now.

Such a declaration can bring more money and other resources to fight a threat but can also trigger economically damaging restrictions on trade and travel in the affected countries, making the decision a politically fraught one.

The decision "should not be taken as a sign that WHO does not think the situation is serious or that we're not taking it seriously. Nothing could be further from the truth," WHO director general Tedros Adhanom Ghebreyesus said. "WHO is following this outbreak every minute of every day."

CONTAINING 11 MILLION IS 'NEW TO SCIENCE'

Authorities have also cancelled "major events" in the capital city indefinitely, including traditional temple fairs that are a staple of holiday celebrations, in order to "execute epidemic prevention and control."

"To my knowledge, trying to contain a city of 11 million people is new to science," Gauden Galea, the World Health Organisation's representative in China, said in an interview.

"It has not been tried before as a public health measure. We cannot at this stage say it will or it will not work."

The Forbidden City – which saw 19 million visitors last year – is usually packed with tourists during the Lunar New Year festival, when hundreds of millions of people travel across China.

Although there have only been more 14 confirmed cases of people infected with the virus so far in Beijing, city authorities have cancelled large-scaled Lunar New Year events this week as part of national efforts to control the spread of the Wuhan virus.

Beijing's city government said they would provide more information "as the epidemic situation evolves."

The illnesses from the newly identified coronavirus first appeared last month in Wuhan, an industrial and transportation hub in central China's Hubei province.

The vast majority of mainland China's more than 570 cases have been in the city. Other cases have been reported in the US, Japan, South Korea and Thailand. Singapore and Hong Kong reported their first cases Thursday. Most illnesses outside China involve people who were from Wuhan or had recently travelled there.

Seventeen people have died, all of them in and around Wuhan. The oldest was 89, the youngest 48.

Images from Wuhan showed long lines and empty shelves at supermarkets, as residents stocked up for what could be weeks of isolation.

That appeared to be an over-reaction, since no restrictions were placed on trucks carrying supplies into the city, although many Chinese have strong memories of shortages in the years before the country's recent economic boom.

Such sweeping measures are typical of China's authoritarian communist government, though the effectiveness of a lockdown against the outbreak remains uncertain.

Local authorities in Wuhan demanded all residents wear masks in public places and urged government staff to wear them at work and shopkeepers to post signs for their visitors, Xinhua news agency reported.

Xinhua quoted the city's antivirus task force as saying the measures were taken in an attempt to "effectively cut off the virus spread, resolutely curb the outbreak and guarantee the people's health and safety."

Liu Haihan left Wuhan last Friday after visiting her boyfriend there. She said everything was normal then, before human-to-human transmission of the virus was confirmed. But things had changed rapidly.

Her boyfriend "didn't sleep much yesterday. He disinfected his house and stocked up on instant noodles," Liu said. "He's not really going out. If he does, he wears a mask."

The sharp rise in illnesses comes as millions of Chinese travel for the Lunar New Year, one of the world's largest annual migrations of people. Chinese are expected to take an estimated 3 billion trips during the 40-day spike in travel. Analysts predicted cases will continue to multiply.

"Even if (cases) are in the thousands, this would not surprise us," the WHO's Galea said, adding, however, that the number of those infected is not an indicator of the outbreak's severity, so long as the mortality rate remains low.

The coronavirus family includes the common cold as well as viruses that cause more serious illnesses, such as the SARS outbreak that spread from China to more than a dozen countries in 2002-03 and killed about 800 people, and Middle Eastern respiratory syndrome, or MERS, which developed from camels.

China is keen to avoid repeating mistakes with its handling of SARS. For months, even after the illness had spread around the world, China parked patients in hotels and drove them around in ambulances to conceal the true number of cases and avoid WHO experts.

In the current outbreak, China has been credited with sharing information rapidly, and President Xi Jinping has emphasised that as a priority.

"Party committees, governments and relevant departments at all levels must put people's lives and health first," Xi said Monday.

"It is necessary to release epidemic information in a timely manner and deepen international co-operation."

Health authorities were taking extraordinary measures to prevent additional person-to-person transmissions, placing those believed infected in plastic tubes and wheeled boxes, with air passed through filters.

The first cases in the Wuhan outbreak were connected to people who worked at or visited a seafood market, which has since been closed for an investigation. Experts suspect that the virus was first transmitted from wild animals but that it may also be mutating. Mutations can make it deadlier or more contagious.

Many countries are screening travellers from China for illness, especially those arriving from Wuhan. North Korea has banned foreign tourists, a step it also took during the SARS outbreak and in recent years because of ebola. Most foreigners going to North Korea are Chinese or travel there through neighbouring China.