Chinese authorities have reported 139 new cases of a mysterious virus in two days, marking the first time that the infection has been confirmed in the country outside of Wuhan city.
The new cases were identified in the cities of Wuhan, Beijing and Shenzhen.
South Korea also reported its first confirmed case of the virus on Monday, following Thailand and Japan.
The total number of confirmed cases now exceeds 200, and three have died from the respiratory illness.
Health officials have identified the infection, which first appeared in Wuhan in December, as being a strain of coronavirus. They say it has led to an outbreak of viral pneumonia, but much about it remains unknown.
Experts in the UK told the BBC the number of people infected could still be far greater than official figures suggest, with estimates closer to 1,700.
China has promised to step up monitoring efforts during this week’s Lunar New Year celebrations, when millions of people will travel to be with their families.
Who has been infected?
Authorities in the central Chinese city of Wuhan said 136 new cases had been confirmed over the weekend, and a third person there died from the virus.
In total, the city alone has confirmed almost 200 cases of the coronavirus. As of late Sunday, officials said 170 people in Wuhan were still being treated in hospital, including nine in critical condition.
Health officials in Beijing’s Daxing district said two people who had travelled to Wuhan were treated for pneumonia linked to the virus.
In Shenzhen, officials said a 66-year-old man showed symptoms of the virus following a trip to visit relatives in Wuhan.
The virus has also spread abroad. Two cases have been confirmed in Thailand and one in Japan – all of them involving people from Wuhan or who had visited the city.
South Korea reported its first confirmed case of the mystery illness on Monday. The Korea Centers for Disease Control and Prevention said a 35-year-old Chinese woman was suffering from a fever and respiratory problems after travelling to the country from Wuhan.
She was put into isolation and treated at a local hospital, they said.
What have health officials said?
China’s National Health Commission on Sunday said the virus was “still preventable and controllable”, while warning that close monitoring was needed given that the source, transmission and mutation methods were unknown.
They said there had been no cases of the virus spreading from one person to another, but that it had instead crossed the species barrier and come from infected animals at a seafood and wildlife market in Wuhan.
The WHO said an “animal source seems the most likely source” of the virus, but that there was “some limited human-to-human transmission occurring between close contacts.”
“As more… cases are identified and more analysis undertaken, we will get a clearer picture of disease severity and transmission patterns,” it wrote on Twitter.
It noted that the rise in cases in China was a result of “increased searching and testing for [the virus] among people sick with respiratory illness”.
People could reduce the risk of catching the coronavirus by taking measures such as avoiding “unprotected” contact with live animals, thoroughly cooking meat and eggs, and avoiding close contact with anyone with colds or flu-like symptoms, it said.
What exactly is this virus?
Viral samples have been taken from patients and analysed in the laboratory, with officials in China and the WHO concluding that the infection is a coronavirus.
Coronaviruses are a broad family of viruses, but only six (the new one would make it seven) are known to infect people.
At the mild end they cause the common cold, but severe acute respiratory syndrome (Sars) is a coronavirus that killed 774 of the 8,098 people infected in an outbreak that started in China in 2002.
Analysis of the genetic code of the new virus shows it is more closely related to Sars than any other human coronavirus.