A leading Hong Kong medical professor warns billions of people could become infected with the deadly coronavirus if the illness is not controlled.
Professor Gabriel Leung, the dean of medicine at the University of Hong Kong and an expert in infectious diseases, told The Guardian the virus - now officially called COVID-19 - could be contracted by more than two-thirds of humans if left unchecked. Currently, 43,000 are infected, with more than 1000 dead from the illness.
Experts believe each infected individual transmits the illness to about 2.5 other people. This gives the illness an "attack rate" of 60 to 80 percent.
"Sixty percent of the world's population is an awfully big number," Prof Leung said.
"Is 60-80 percent of the world's population going to get infected? Maybe not. Maybe this will come in waves. Maybe the virus is going to attenuate its lethality because it certainly doesn't help it if it kills everybody in its path, because it will get killed as well."
With a global population of 7.8 billion and an infection rate of 60 percent, 4.6 billion people would become infected. A death rate of 1 percent of the infected would mean 46 million would die.
The professor's comments come after the World Health Organisation's director Tedros Adhanom Ghebreyesus said the known number of cases of coronavirus patients who had never visited China was just "the tip of the iceberg".
The illness has spread from the epicentre of Wuhan, China to more than 25 countries, including Australia, United States, and the United Kingdom. There have been no confirmed cases in New Zealand.
"The detection of a small number of cases may indicate more widespread transmission in other countries; in short, we may only be seeing the tip of the iceberg," said Ghebreyesus.
Many countries - like New Zealand - have put stringent rules in place to stop the transmission of the disease, including blocking Chinese tourists from entering the country. China has gone as far as to put infected people into quarantine camps and threaten those who don't isolate themselves with harsh penalties.
Prof Leung wants to know whether restrictions imposed in Wuhan have worked to stop the virus' spread. If so, he says they should be rolled out in other centres.
"Let's assume that they have worked. But how long can you close schools for? How long can you lock down an entire city for? How long can you keep people away from shopping malls?" he told The Guardian.
"If you remove those [restrictions], then is it all going to come right back and rage again? So those are very real questions."
If the restrictions haven't worked, he suggests focus should be on looking at ways to contain the virus, rather than developing vaccines. A vaccine isn't expected to be developed for 18 months.
Those who have travelled to China are asked to self-isolate for at least 14 days and look out for symptoms.
"Common signs of infection include respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. In more severe cases, infection can cause pneumonia, severe acute respiratory syndrome, kidney failure and even death," the WHO says.
"Standard recommendations to prevent infection spread include regular hand washing, covering mouth and nose when coughing and sneezing, thoroughly cooking meat and eggs. Avoid close contact with anyone showing symptoms of respiratory illness such as coughing and sneezing."