The number of people infected by a mystery SARS-like virus that has killed two people in China is likely to be hundreds more than officially reported, researchers have said.
The news comes as Chinese health authorities said on Saturday that they have discovered four more cases of pneumonia following an outbreak of what is believed to be a new coronavirus strain.
The four individuals were diagnosed with pneumonia on Thursday and are in stable condition, the Wuhan Municipal Health Commission said in a statement published shortly after midnight.
Saturday's statement marked the first confirmation of new cases by officials in nearly a week and came a day after the commission confirmed the death of a second patient.
Coronaviruses usually cause mild to moderate upper-respiratory tract illnesses, such as the common cold, but can also affect the lower-respiratory tract, causing pneumonia or bronchitis.
Chinese authorities said 45 people in the country had contracted the virus, with the outbreak centred around a seafood market in the central city of Wuhan, which is home to 11 million people.
"[The Chinese government] has released figures saying there are 45 people affected, about 100 people continue to be monitored, 600 who were originally quarantined have now been let go because they have no symptoms," Al Jazeera's Katrina Yu, reporting from Beijing, said.
But a paper published on Friday by scientists with the MRC Centre for Global Infectious Disease Analysis at Imperial College London said the number of those affected in the city was likely to be considerably more than a thousand.
The scientists at the centre - which advises bodies including the World Health Organization (WHO) - said they estimated a "total of 1,723 cases" in Wuhan would have been infected as of January 12.
The researchers took the number of cases reported outside China so far - two in Thailand and one in Japan - to construe how many people were likely infected in Wuhan, based on international flight traffic data from the city's airport. _Agencies