China has confirmed cases of human-to-human transmission in the outbreak of a new SARS-like virus as the number of cases soared and the World Health Organisation said it would consider declaring an international public health emergency.

The coronavirus, which has spread to three other Asian countries and infected more than 200 people in China, has caused alarm because it of its genetic similarities to Severe Acute Respiratory Syndrome (SARS), which killed nearly 650 people across mainland China and Hong Kong in 2002-03.

The discovery of human-to-human transmission comes as hundreds of millions of people are criss-crossing the country in packed trains, buses and planes this week to celebrate the Lunar New Year with relatives.

Health authorities in the central city of Wuhan, where a seafood market has been identified as the centre of the outbreak, said on January 21 that an 89-year-old man became the fourth person to die from the virus and that 15 medical staff had been infected. A second case was confirmed in Shanghai, while five people have been diagnosed with the virus in Beijing.

Zhong Nanshan, a renowned scientist at the national health commission, confirmed that the virus was being transmitted between humans, state media reported on January 20.

WHO had previously identified animals as the likely primary source, but had warned of “some limited human-to-human transmission”.

WHO said a key emergency committee would meet on January 22 to determine whether to declare an international public health emergency.

The agency has only used the rare label a handful of times, including during the H1N1 - or swine flu - pandemic of 2009 and the Ebola epidemic that devastated parts of West Africa from 2014 to 2016.

The Chinese government announced on January 21 it was classifying the outbreak in the same category as the SARS outbreak, meaning compulsory isolation for those diagnosed with the disease and the potential to implement quarantine measures on travel.

Chinese President Xi Jinping said that the virus must be “resolutely contained” and stressed that information must be released “in a timely manner”, in his first public comments on the outbreak.

The communist government was accused of covering up the SARS outbreak in 2003, but some foreign experts praised the swift release of information on the new virus.

“The speed of response is testimony to improved global preparedness,” said Jeremy Farrar, director of British healthcare foundation Wellcome Trust. “But we must not be complacent, there is still much to be done to ensure countries across the world are protecting people from epidemic threats of diseases known and unknown.”

Nearly 200 confirmed cases are in Wuhan, where the city announced it was enforcing stronger supervision of markets and public transportation hubs, and “encouraged the cancellation” of unnecessary public gatherings.

The city has set up an epidemic prevention and control headquarters.

A handful of cases have also been reported in neighbouring countries. A 35-year-old woman who flew in from Wuhan was confirmed as the first case in South Korea. Thailand and Japan have previously confirmed a total of three cases - all of whom had visited Wuhan.

Special screening measures have been set up at airports in Australia, Singapore, the US and Thailand.

In Hong Kong, health officials said they were expanding enhanced checks on arrivals to include anyone coming in from Hubei province, not just its capital Wuhan.

Scientists with the MRC Centre for Global Infectious Disease Analysis at Imperial College in London warned that the number of cases in Wuhan was likely to be closer to 1,700, much higher than the official figure.

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