An expert advisor to the World Health Organization (WHO) has described the coronavirus outbreak as potentially "thermonuclear pandemic level bad".

Dozens have been killed by the virus 2019-nCoV since it was first detected in early December, and as of Sunday morning (NZ time) there were 1441 confirmed cases.

But research into the disease - which at present has no vaccine, and might not for months - has doctors worried. Some have estimated for every person that gets infected, they will infect up to four more.

Others have come to figures of 3.8, 3.3, and 2.6, all above the WHO's estimate of between 1.4 and 2.5.

It's also been discovered people can carry the virus without showing symptoms, doctors calling them "cryptic cases of walking pneumonia".

Only 5.1 percent of all cases in Wuhan have been identified, researchers in the UK estimate, with perhaps more than 11,000 infected by January 21.

"HOLY MOTHER OF GOD," Dr Eric Feigl-Ding wrote on his Twitter account on hearing the news.

"It is thermonuclear pandemic level bad... I'm not exaggerating."