Coronavirus has already killed more people in seven weeks than Ebola has killed in the second-worst outbreak in the Democratic Republic of Congo in nearly two years, according to the World Health Organisation.
Dr Margaret Harris of the WHO told ABC's 7.30 the virus was causing so much concern because of its ability to infect very large numbers of people.
On the mortality rate, which was recently updated to 3.4 per cent of all cases, Harris said: "That is a huge number of people."
Harris said the reason the virus had spread faster in some countries over others was because people were very close together, with denser populations.
"They don't really have the opportunity to do what we call 'social distancing' - that's keeping a couple of metres away from people when you've got a contagious virus like this spreading," she said.
"It is a lot easier in Australia than it is, say, for instance, in Wuhan in China."
Harris was asked what she would say to suggestions the WHO was slow off the mark containing the virus because it was cutting China some slack because it was a major donor to the organisation, news.com.au reported.
"None of that's true," she said.
• Coronavirus case: 'Terrified' grandmother worried she's infected others
• Coronavirus: New Zealand's second confirmed case of virus flew domestically
• Coronavirus: Family of NZ woman with virus 'battered' on social media
• Ministry of Health confirms NZ has two coronavirus cases
"And we weren't slow off the mark. It's interesting, WHO is everybody's favourite whipping boy and we accept that, you know, we always want to do better and if people criticise us, it helps us to do better.
"But, no, we weren't slow off the mark. They notified us in December. We had people in there, we've got a large country office, they were very, very open and one of the main reasons we know what this virus is, and had a test in a couple of weeks, was because China shared that data. In fact, this has never happened in an outbreak of a new virus before. It is unprecedented."
Dr Niall Ferguson, one of the world's best-known historians, said the coronavirus would not be as bad as the Black Death of the 14th Century or the 1918/19 influenza pandemic which probably killed more people than World War I.
"But it does seem certain to be more economically disruptive than any of the more recent pandemics since World War II," he said.
"There have been some big influenza pandemics, then there was Sars, which in some
ways resembles this new coronavirus. It was more lethal but did not spread so far and did not cause as much economic disruption."
He said what happened in 1918/19 illustrated how enormously dangerous a mutant virus could be to humanity.
"Because if you think about the numbers who were affected, and that runs to the tens of millions on any estimate of killed, then this is in some ways the biggest danger that we face as a species, aside, perhaps, from nuclear war, because it can happen so swiftly.
"Now, medical science has made great advances in the past century, so we're better equipped than the people of 1918/19.
"On the other hand, the world has got much more interconnected and travel times have been drastically reduced, so in that sense, I think we are very vulnerable."