China has confirmed that the deadly Wuhan coronavirus virus can be transmitted between humans, with medical workers currently among the infected.
The virus causes symptoms of viral pneumonia, and has already led at least 17 deaths – although officials have said those appear to be where patients had other, underlying health conditions.
Little is known about the new disease which, if confirmed, would be only the seventh coronavirus known to science that can infect humans.
Here’s what we do know about the disease, currently dubbed 2019-nCoV or simply novel coronavirus.
What is coronavirus? And what are the symptoms?
Coronaviruses are a group of virus that cause respiratory infections – diseases ranging from the common cold to SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome). This is the seventh known to infect humans.
SARS first infected people in southern China in late 2002 and spread to more than two dozen countries, killing nearly 800. The Chinese government initially tried to conceal the severity of the SARS epidemic, but its cover-up was exposed by a high-ranking physician.
The virus causing the current outbreak is different from those previously identified, Chinese scientists said earlier this month. Initial symptoms of the novel coronavirus are mainly fever, health officials said, with some experiencing coughing, tightness of the chest and shortness of breath. Scans on some patients have shown fluid in the lungs consistent with viral pneumonia.
The World Health Organisation (WHO), which was first informed of the cluster of illness in Wuhan on 31 December, said the new disease was isolated for study on 7 January after other causes such as SARS, avian flu and MERS had been ruled out. It said it was closely following the current outbreak.
Is it contagious?
Authorities initially believed that every confirmed case was linked to the seafood market in Wuhan, and that hundreds of people who came into close contact with diagnosed patients were not infected themselves, leading the municipal health commission to maintain that the virus is not easily transmitted between humans.
However, China's National Health Commission confirmed on Monday the first examples of the deadly virus spreading from human to human.
Zhong Nanshan, a respiratory expert, said two people in Guangdong province in southern China caught the disease from family members, state media said.
Zhong said the two people in Guangdong had not been to Wuhan but family members had returned from the city.
The announcement followed a sharp rise in the number of cases over the weekend, with some of those who fell ill having no direct link to the market.
How has China responded?
China has now placed the city of Wuhan on lockdown, and insists the country is putting forth its “utmost efforts to tackle the situation”, the Chinese foreign ministry spokesman Geng Shuang said on Monday.
In addition to promptly raising the issue with the WHO, the government has notified and stayed in contact with other countries in the region.
Some have taken voluntary measures to reduce their risk, with the country currently undergoing the world’s largest human migration as people travel to celebrate the Lunar New Year.
According to posts on the Weibo social media platform, people are sharing prevention advice such as wearing masks and washing hands, eating lightly and avoiding crowded places. Others said they had cancelled their New Year travel plans.
State media praised the apparent evolution of the official response since the deadly SARS outbreak 17 years ago.
“In the early days of SARS, reports were delayed and covered up,” said an editorial in the state-run Global Times. “That kind of thing must not happen again in China.”
“We have made great strides in medicine, social affairs management and public opinion since 2003,” the editorial added.
The WHO said it was reassured by the authorities’ response, and that it did not see the need for any further recommendations against travel to China at this time.
And what about outside China?
At least half a dozen countries in Asia, several US airports and Heathrow have started screening incoming airline passengers from central China.
Videos posted online showed people in protective suits checking one by one the temperatures of plane passengers arriving in Macao, a Chinese special administrative region, from Wuhan. A man surnamed Yang who works for the Macao Health Bureau confirmed over the phone that such checks are indeed taking place in the southern Chinese region.
Authorities in Thailand and Japan have already identified at least three cases, all involving recent travel from China. The WHO said contact-tracing efforts were under way and, in Japan, the government was coordinating across ministries to assess and contain the risk of outbreak.
South Korea reported its first case on Monday, when a 35-year-old Chinese woman from Wuhan tested positive for the new coronavirus one day after arriving at Seoul’s Incheon airport. The woman has been isolated at a state-run hospital in Incheon city, just west of Seoul, the Korea Centers for Disease Control and Prevention said in a statement.
Additional reporting by agencies