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A crucial question for how the outbreak will unfold is how contagious the virus is. Scientists around the world are trying to establish how many people, on average, each infected person will pass the virus on to, a number known as R0 in epidemiology. If this number is more than one, an epidemic will grow and if less than one it will fizzle out.

An analysis posted online on Friday by scientists from Lancaster University puts R0 for the new coronavirus at 3.8 and estimates that should the epidemic continue unabated, there could be 191,529 infections by 4 February.

The paper also suggests that travel restrictions from and to Wuhan city are unlikely to be effective in halting transmission across China. The analysis assumes that only 5% of infections in Wuhan have been identified, which would imply a far larger pool of people whose symptoms have been mild and who have not attended hospital. So while more people may have been infected than initially thought, on the positive side, it would imply that the majority of infections do not cause severe symptoms.