During that time, an asymptomatic person is also infectious and could spread the coronavirus to others, Ma said, which makes it difficult to stop its spread.
"At present, the rate of development of the epidemic is accelerating," Ma said at the press conference. "I am afraid that it will continue for some time, and the number of cases may increase."
The virus, which originated in Wuhan, China, has killed 56 people and infected more than 2,000, Reuters reported on Sunday.
Although officials have quarantined Wuhan and some other neighbouring cities, the virus has spread to at least 12 other countries: Thailand, Japan, South Korea, Taiwan, Vietnam, Singapore, Nepal, France, Australia, Malaysia, Canada, and the US.
Currently, there are no tests designed to detect this exact coronavirus strain, since 'coronavirus' refers to a family of viruses that cause common colds, Chiu said, and current coronavirus tests that doctors use can't detect the Wuhan coronavirus strain.
Someone who gets a coronavirus could have minor symptoms and develop a flu or develop a more severe or life-threatening condition like pneumonia.
Others viruses are infectious before symptoms appear
The Wuhan coronavirus isn't the only viral infection that is infectious before a person shows symptoms.
According to the National Health Service in the UK, chickenpox, the common cold, and the flu are all infectious multiple days before a person with the virus shows any symptoms, like a rash in the case of chickenpox or a fever for the flu.
This article was originally published by Business Insider.
More from Business Insider: