China reported 17 new cases of a mysterious virus on Sunday, including three patients in a severe condition, heightening concerns of more infections as hundreds of millions of people prepare to travel home for the Lunar New Year holiday.

The new strain of coronavirus has caused alarm because of its connection to Severe Acute Respiratory Syndrome, or SARS, which started in southern China in late 2002 and spread to over 24 countries, killing nearly 800 people.

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Of the 17 new cases in the central city of Wuhan - believed to be the epicentre of the outbreak - three were described as "severe" with two of those patients too critical to be moved, authorities said.

Those infected range from 30 to 79 years old.

The virus has now infected 62 people in Wuhan, city authorities said, with eight in a severe condition, 19 cured and discharged from hospital and the rest in isolation receiving treatment.

Two people have died from the virus, including a 69-year-old man who died on Wednesday after the disease caused pulmonary tuberculosis and damaged multiple organ functions.

Authorities said they had begun "optimised" testing of pneumonia cases across the city to identify those infected, and would begin "detection work... towards suspected cases in the city" as a next step, as well as carrying out "sampling tests".

Scientists with the MRC Centre for Global Infectious Disease Analysis at Imperial College in London warned in a paper published on Friday that the number of cases in the city was likely to be closer to 1,700, much higher than the number officially identified.

Authorities said on Sunday that some of the cases had "no history of contact" with the seafood market believed to be the centre of the outbreak.

No human-to-human transmission has been confirmed so far, but Wuhan's health commission has previously said the possibility "cannot be excluded".

Airport screening

A handful of cases have also been reported overseas in Thailand, Japan and Singapore, which has said it has five suspected infections among people who had travelled to Wuhan.

People in Japan often wear masks during the winter or when they are sick. Japan reported on Thursday that a man treated for pneumonia after returning from China had tested positive for a new coronavirus [Eugene Hoshiko/ AP Photo]

Those countries' airports are among at least half a dozen in Asia, as well as New York's JFK, San Francisco and Los Angeles airports in the United States, that have started screening incoming airline passengers from central China.

In China itself, there has been no official announcement of screening measures, but Wuhan deputy mayor Chen Xiexin told state broadcaster CCTV that infrared thermometers had been installed at airports, railway stations and coach stations across the city.

Chen said passengers with fevers were being registered, given masks and taken to medical institutions, and nearly 300,000 body temperature tests had been carried out, according to CCTV.

Screening has also been stepped up in Hong Kong, with temperature checkpoints introduced for inbound travellers from the Chinese mainland.

About 11 million people live in Wuhan and the city serves as a major transport hub, including during the annual Lunar New Year holiday, when hundreds of millions of Chinese people travel across the country to visit family.